Abrasive and Abrasion Minerals

Topic 2: Abrasive and Abrasion Minerals
Hassan Z. Harraz
hharraz2006@yahoo.com
2015- 2016
Prof. Dr. H.Z. Harraz Presentation Abrasive Minerals

Outline of Topic 2:
We will explore all of the above in Topic 2.
 Abrasive
 Factors Affecting Rate of Abrasion
 Good Abrasive
 Classification of Abrasives
 Abrasive Minerals
 Types of Abrasive minerals
 Nature Abrasive Minerals
 Synthetic Abrasive Minerals
 Selected Nature and Synthetic Abrasive Minerals
21 November 2015 Prof. Dr. H.Z. Harraz Presentation Abrasive Minerals 2

Defined
 Abrasives are substances that are used to clean or dress the
surfaces of other minerals, or comminute materials by abrasion and
percussion.
 An abrasive is a type of very hard material, (it can often be a
mineral).
 Abrasives may be classified as either natural or synthetic.
 Abrasives are shaped for various purposes.
 Abrasives are used in a wide range of domestic, industrial and
technological applications.
 Abrasives are used to finish or shape a work piece. Rubbing the
abrasive on the work piece leads to part of the work piece being
worn away. When finishing a material it is often thought of as a
means to polish the material to gain a smooth surface or even
reflective surface; however some finishes require roughening as in
beaded, matte or satin finishes.

Abrasive Materials
 Natural materials are divided into three groups:
1) High-grade natural abrasives, which include, in order of
hardness: Diamond, Corundum, Emery, and Garnet.;
2) Siliceous abrasives, consisting of various forms of silica; and
3) Miscellaneous abrasives, including buffing and polishing
powders.
High-grade natural
abrasives
Siliceous abrasives Miscellaneous abrasives
Diamond Sandstone Bauxite Silicon carbide (Trade names of Carborundum)
Corundum Quartzite Magnesite Fused alumina (Trade names of Alundum and
Aloxite)
Emery (mixture of
corundum and magnetite)
Novaculite Magnesium oxide Boron carbide
Garnet Flint Ground Feldspar Metallic oxides
Chert Chalk Lampblack
Silicified Limestone Lime Carbon black
Quartz China Clay
Sand Talc
Tripoli Tin oxide
Pumice Manganese oxide
Diatomite Chromium oxide
Iron oxide

Type of Abrasives
 Abrasives are structured for individual purposes.
 Generally abrasives can be classified into synthetic or natural.
 When discussing sharpening stones, natural stones have long been considered superior but advances in material
technology are seeing this distinction become less distinct.
 Many synthetic abrasives are effectively identical to a natural mineral, differing only in that the synthetic mineral has
been manufactured rather than been mined.
 Impurities in the natural mineral may make it less effective.
 Natural abrasives:
 Many minerals and rocks of diverse composition but with one thing in common “Hardness”
 are used in the natural state, except for processing and bonding.
 may be used: i) in natural form (example: Sand, Pumice); ii) after shaping (example millstone); and iii)
after being ground into grains or powders and made up into wheels or papers.
 are often sold as dressed stones, usually in the form of a rectangular block.
 Natural diamonds are used primarily in diamond-tipped drill bits and saw blades for cutting or shaping
rock, concrete, grinding wheels, glass, quartz, gems, and high-speed tool steels.
 Other naturally occurring abrasive materials (including garnet, emery, silica sand, and quartz) are used
in finishing wood, leather, rubber, plastics, glass, and softer metals.
 Synthetic abrasives
 Many synthetic abrasives are productively equivalent to an organic mineral.
 It differs only in the fact that synthetic minerals are manufactured instead of mined.
 The largest application of synthetic diamonds has been in wheels for grinding carbides and ceramics.
 Both natural and synthetic abrasives are commonly available in a wide variety of shapes, often coming as bonded or
coated abrasives, including blocks, belts, discs, wheels, sheets, rods and loose grains.
 Manufactured abrasives are classified into three types namely: coated, bonded and super abrasives.

Naturally Abrasives Synthetic Abrasives
Coarse Abrasives Soft Scrubbing
Powders
Soft Abrasives
Diamond dust Diatomite Ground Feldspar Silicon carbide (Carborundum)
Emery (impure corundum) Pumice Chalk Tungsten Carbide
TripoliCorundum Kaolin Boron carbide
Garnet Calcite Borazon (Cubic Boron Nitride
”CBN”)Sand
Rouge (Fe2O3) Ceramic (FeO, MgO, Cr2O3, MnO,
TiO2, Al2O3)Sandstone
Staurolite Dry ice
Novaculite Glass powder
Steel abrasive
Zirconia alumina
Slags
Diamonds (synthetic diamonds)
21 November Prof. Dr. H.Z. Harraz Presentation Abrasive Minerals 6

Range of Abrasive Selling Prices

i) Bonded Abrasives
 A bonded abrasive is composed of an abrasive material contained within a matrix,
although very fine aluminium oxide abrasive may comprise sintered material.
 This matrix is called a binder and is often a clay, a resin, a glass or a rubber.
 This mixture of binder and abrasive is typically shaped into blocks, sticks, or wheels.
 The most usual abrasive used is aluminium oxide (Al2O3), silicon carbide (SiC),
tungsten (IV) carbide (WC) and garnet.
 Artificial sharpening stones are often a bonded abrasive and are readily available as
a two sided block, each side being a different grade of grit.
 Bonded Abrasives are required to be dressed after they are used.
Assorted grinding wheels as
examples of bonded abrasives.
A grinding wheel with a reservoir to
hold water as a lubricant and
coolant
Honing

ii) Coated Abrasives
 Coated Abrasives are also minerals that are used in the same way as bonded
abrasives.
 A coated abrasive is an abrasive fixed on to a form of backing material like paper,
metal, rubber, resin, cloth and polyester.
 A bonding agent (often some sort of adhesive or resin) is applied to the backing to
provide a flat surface to which the grit is then subsequently adhered. A woven
backing may also use a filler agent (again, often a resin) to provide additional
resilience.
 Sandpaper is a best example of coated abrasive. Sandpaper is a very common
coated abrasive.
 Coated abrasives may be shaped for use in rotary and orbital sanders, for wrapping
around sanding blocks, as handpads, as closed loops for use on belt grinders, as
striking surfaces on matchboxes, on diamond plates and diamond steels. Diamond
tools, though for cutting, are often abrasive in nature.
A German sandpaper showing its backing and
FEPA grit size.

iii) Super Abrasives
 Super Abrasives are one of a group of relatively expensive but effective materials
possessing superior hardness and abrasion resistance.
 Super Abrasives include Borazon (Cubic Boron Nitride ”CBN”) and diamond.
 Super Abrasives have been developed to meet the needs of modern industry.
 CBN next hardest substance to diamond (i.e., its hardness is 14 Mohos, scale), CBN
is replacing the diamond and diamond dust for many abrasive purposes.
 CBN is used for machining the hardest steels to precise forms and finishes.

Abrasives Manufacturing
General
 The abrasives industry is composed companies engaged in the following separate types of
manufacturing:
 Abrasive grain manufacturing : produce materials for use by the other abrasives
manufacturers to make abrasive products.
 Bonded abrasives product manufacturing : is very diversified and includes the
production of grinding stones and wheels, cutoff saws for masonry and metals, and other
products.
 Coated abrasive product manufacturing : include those facilities that produce large rolls
of abrasive-coated fabric or paper, known as jumbo rolls, and those facilities that
manufacture belts and other products from jumbo rolls for end use.

Abrasive Grain Processing
 Abrasive grains for both bonded and coated abrasive
products are made by graded crushing and close
sizing of either natural or synthetic abrasives.
 Raw abrasive materials first are crushed by primary
crushers and are then reduced by jaw crushers to
manageable size, approximately 19 mm.
 Final crushing is usually accomplished with roll
crushers that break up the small pieces into a usable
range of sizes.
 The crushed abrasive grains are then separated into
specific grade sizes by passing them over a series of
screens.
 If necessary, the grains are washed in classifiers to
remove slimes, dried, and passed through magnetic
separators to remove iron-bearing material, before the
grains are again closely sized on screens. This careful
sizing is necessary to prevent contamination of grades
by coarser grains.
 Sizes finer than 0.10 mm are separated by hydraulic
flotation and sedimentation or by air classification.
Figure -1. Process flow diagram for abrasive grain
processing

Abrasive Grain Manufacturing
• The most commonly used abrasive materials are aluminum oxides (Al2O3) and silicon carbide (SiC).
These synthetic materials account for as much as 80 to 90 % of the total quantity of abrasive grains
produced domestically. Other materials used for abrasive grains are Borazon (cubic boron nitride: CBN),
synthetic diamonds, and several naturally occurring minerals such as garnet and emery. The use of
garnet as an abrasive grain is decreasing.
• The following paragraphs describe the production of aluminum oxide, silicon carbide, CBN, and synthetic
diamond.
a) Silicon carbide (SiC):
• is known under trade names Carborundum, Crystalon, and carbolon. Its hardness is 13 Mohos
, scale.
• is used mainly in cutting wheels and papers and cloths.
• is produced in large tonnages using the Acheson process by reacting of about 60 % high-purity silica
sand and 40 % finely ground low-sulfur coke in a resistance electric arc furnace for 36 hours at 2200-
2500oC .
SiO2 + 3C → SiC + 2CO(gas)
• A small amount of sawdust is added to the mix to increase its porosity so that the carbon monoxide
(CO) gas formed during the process can escape freely.
• Common salt is added to the mix to promote the carbon-silicon reaction and to remove impurities in the
sand and coke.
 During the heating period, the furnace core reaches approximately 2200°C, at which point a large
portion of the load crystallizes.
 At the end of the run, the furnace contains a core of loosely knit silicon carbide crystals surrounded by
unreacted or partially reacted raw materials.
 The silicon carbide crystals are removed to begin processing into abrasive grains.
• The crystalline product is crushed, washed in acid and alkali, and then dried after iron has been
removed magnetically.
• Granular material is used in refractories and bonded abrasives.

Abrasive Grain Manufacturing
b) Fused aluminum oxide (Al2O3)
 Fused alumina is trade names of Alundum and Aloxite.
 Before processing, bauxite, the crude raw material, is calcined at about 950°C to remove both free and
combined water.
 The bauxite is then mixed with ground coke (~3 %) and iron borings (~2 %) in a pot-type, electric-arc
furnaces for 24 hours at 2000oC.
 An electric current is applied and the intense heat, on the order of 2000oC, melts the bauxite and
reduces the impurities that settle to the bottom of the furnace.
 As the fusion process continues, more bauxite mixture is added until the furnace is full.
 The furnace is then emptied and the outer impure layer is stripped off.
 The core of aluminum oxide is then removed to be processed into abrasive grains.
c) Cubic Boron Nitride ”CBN”
 is trade names of Borazon
 is synthesized in crystal form from hexagonal boron nitride, which is composed of atoms of boron and
nitrogen.
 The hexagonal boron nitride is combined with a catalyst such as metallic lithium at temperatures in the
range of 1650°C and pressures of up to 1,000,000 pounds per square inch [psi].
d) Synthetic Diamond.
 is manufactured by subjecting graphite in the presence of a metal catalyst to pressures in the
range of 808,000 to 1,900,000 psi at temperatures in the range of 1400 to 2500°C.

Bonded Abrasive Products Manufacturing
 The grains in bonded abrasive products are held together by one of six
types of bonds: vitrified or ceramic (which account for more than
50 % of all grinding wheels), resinoid (synthetic resin), rubber,
shellac, silicate of soda, or oxychloride of magnesium.
 Figure 2 presents a process flow diagram for the manufacturing of
vitrified bonded abrasive products.
 Measured amounts of prepared abrasive grains are moistened and
mixed with porosity media and bond material.
 Porosity media are used for creating voids in the finished wheels and
consist of filler materials, such as paradichlorobenzene (moth ball
crystals) or walnut shells, that are vaporized during firing.
 Feldspar and clays generally are used as bond materials in vitrified
wheels.
 The mix is moistened with water or another temporary binder to make
the wheel stick together after it is pressed.
 The mix is then packed and uniformly distributed into a steel grinding
wheel mold, and compressed in a hydraulic press under pressures
varying from 150 to 10,000 psi. If there is a pore-inducing media in the
mix such as paradichlorobenzene, it is removed in a steam autoclave.
Prior to firing, smaller wheels are dried in continuous dryers; larger
wheels are dried in humidity-controlled, intermittent dry houses.
 Most vitrified wheels are fired in continuous tunnel kilns in which the
molded wheels ride through the kiln on a moving belt. However, large
wheels are often fired in bell or periodic kilns. In the firing process, the
wheels are brought slowly to temperatures approaching 1400°C for as
long as several days depending on the size of the grinding wheels and
the charge. This slow temperature ramp fuses the clay bond mixture so
that each grain is surrounded by a hard glass-like bond that has high
strength and rigidity. The wheels are then removed from the kiln and
slowly cooled.
Figure 2. Process flow diagram for the manufacturing
of vitrified bonded abrasive products.

Bonded Abrasive Products Manufacturing (Cont. )
• After cooling, the wheels are checked for distortion, shape, and size. The wheels are then machined to final size,
balanced, and overspeed tested to ensure operational safety. Occasionally wax and oil, rosin, or sulfur are applied
to improve the cutting effectiveness of the wheel.
• Resin-bonded wheels are produced similarly to vitrified wheels. A thermosetting synthetic resin, in liquid or powder
form, is mixed with the abrasive grain and a plasticizer (catalyst) to allow the mixture to be molded. The mixture is
then hydraulically pressed to size and cured at 150 to 200°C for a period of from 12 hours to 4 or 5 days
depending on the size of the wheel.
• During the curing period, the mold first softens and then hardens as the oven reaches curing temperature. After
cooling, the mold retains its cured hardness. The remainder of the production process is similar to that for vitrified
wheels.
• Rubber-bonded wheels are produced by selecting the abrasive grain, sieving it, and kneading the grain into a
natural or synthetic rubber. Sulfur is added as a vulcanizing agent and then the mix is rolled between steel
calendar rolls to form a sheet of the required thickness. The grinding wheels are cut out of the rolled sheet to a
specified diameter and hole size. Scraps are kneaded, rolled, and cut out again. Then the wheels are vulcanized in
molds under pressure in ovens at approximately 150 to 175°C. The finishing and inspection processes are similar
to those for other types of wheels.
• Shellac-bonded wheels represent a small percentage of the bonded abrasives market. The production of these
wheels begins by mixing abrasive grain with shellac in a steam-heated mixer, which thoroughly coats the grain
with the bond material (shellac). Wheels 3 mm thick or less are molded to exact size in heated steel molds.
Thicker wheels are hot-pressed in steel molds.
• After pressing, the wheels are set in quartz sand and baked for a few hours at approximately 150°C. The finishing
and inspection processes are similar to those for other types of wheels.
• In addition to grinding wheels, bonded abrasives are formed into blocks, bricks, and sticks for sharpening and
polishing stones such as oil stones, scythe stones, razor and cylinder hones. Curved abrasive blocks and abrasive
segments are manufactured for grinding or polishing curved surfaces.
• Abrasive segments can also be combined into large wheels such as pulpstones. Rubber pencil and ink erasers
contain abrasive grains; similar soft rubber wheels, sticks, and other forms are made for finishing soft metals.

Coated Abrasive Products Manufacturing
 Coated abrasives consist of sized abrasive grains held by a film of
adhesive to a flexible backing.
 The backing may be film, cloth, paper, vulcanized fiber, or a
combination of these materials.
 Various types of resins, glues, and varnishes are used as adhesives
or bonds.
 The glue is typically animal hide glue. The resins and varnishes are
generally liquid phenolics or ureas, but depending on the end use of
the abrasive, they may be modified to yield shorter or longer drying
times, greater strength, more flexibility, or other required properties.
 Figure 3 presents a process flow diagram for the manufacturing of
coated abrasive products.
 The production of coated abrasive products begins with a length of
backing, which is passed through a printing press that imprints the
brand name, manufacturer, abrasive, grade number, and other
identifications on the back. Jumbo rolls typically are 1.3 m wide by
1,372 m in length. The shorter lengths are used for fiber-backed
products, and the longer lengths are used for film-backed abrasives.
 Then the backing receives the first application of adhesive bond, the
"make" coat, in a carefully regulated film, varying in concentration
and quantity according to the particle size of the abrasive to be
bonded.
 Next, the selected abrasive grains are applied either by a mechanical
or an electrostatic method.
 Virtually all of the abrasive grain used for coated abrasive products is
either silicon carbide or aluminum oxide, augmented by small
quantities of natural garnet or emery for woodworking, and minute
amounts of diamond or CBN.
Figure 3. Process flow diagram for the manufacturing
of coated abrasive products.

Coated Abrasive Products Manufacturing (Cont.)
• In mechanical application, the abrasive grains are poured in a controlled stream onto the
adhesive-impregnated backing, or the impregnated backing is passed through a tray of abrasive
thereby picking up the grains.
• In the electrostatic method, the adhesive-impregnated backing is passed adhesive-coated side
down over a tray of abrasive grains, while at the same time passing an electric current through the
abrasive. The electrostatic charge induced by the current causes the grains to imbed upright in the
wet bond on the backing. In effect the sharp cutting edges of the grain are bonded perpendicular
to the backing. It also causes the individual grains to be spaced more evenly due to individual
grain repulsion. The amount of abrasive grains deposited on the backing can be controlled
extremely accurately by adjusting the abrasive stream and manipulating the speed of the backing
sheet through the abrasive.
• After the abrasive is applied, the product is carried by a festoon conveyor system through a drying
chamber to the sizing unit, where a second layer of adhesive, called the size coat or sand size,
is applied.
• The size coat unites with the make coat to anchor the abrasive grains securely.
• The coated material is then carried by another longer festoon conveyor through the final drying
and curing chamber in which the temperature and humidity are closely controlled to ensure
uniform drying and curing. When the bond is properly dried and cured, the coated abrasive is
wound into jumbo rolls and stored for subsequent conversion into marketable forms of coated
abrasives.
• Finished coated abrasives are available as sheets, rolls, belts, discs, bands, cones, and many
other specialized forms.

Applications of Abrasives
 Abrasives have a wide application in all phases of industry, and their use rises and falls with
industrial trends.
 Abrasives used in the soap industry (including scouring soap) include: pumice, feldspar, diatomite,
bentonite, talc, silica, chalk and clays.
 Metal polishes use pumice, emery, diatomite, silica, Tripoli, chalk, clay, bauxite.
 Aluminum Oxide is the most common mineral used in sandpapers, grinding wheels, cut-off tools
and other 3M abrasive products.
 Many of the materials that serve as abrasives have greater use for other purposes. Natural
abrasives are being supplanted by artificial abrasives.
 Common applications for abrasives include the following:
 Buffing (Tripoli)
 Honing
 Drilling (Industrial Diamonds, Carbonados; Bort)
 Grinding
 Sanding
 Polishing
 Cutting
 Sharpening

Abrasive
 An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing
which leads to part of the workpiece being worn away. While finishing a material often
means polishing it to gain a smooth, reflective surface it can also involve roughening as in satin, matte
or beaded finishes.
 Abrasives are extremely common place and are used very extensively in a wide variety of industrial,
domestic, and technological applications. This gives rise to a large variation in the physical and chemical
composition of abrasives as well as the shape of the abrasive. Common uses for abrasives
include grinding, polishing, buffing, honing, cutting, drilling, sharpening, lapping, and sanding
ABRASION: is the process of wear of a material by another material through scratching, chiseling or other
mechanical means.
ABRASIVE:
 is a material, often a mineral, that is used to shape or finish a work-piece through rubbing which
leads to part of the work-piece being worn away
 is a hard substance used for grinding, finishing or polishing of a less hard surface, or the
material that causes wear is called abrasive.
SUBSTRATE: The material being abraded is called a substrate.
P.S ABRASIVE IS HARDER THAN THE SUBATRATE.
EROSION: Is caused by hard particles impacting a substrate surface, carried by a stream of either liquid or
air e.g. sandblasting.
BULK REDUCTION: Is the process of removing excess material by cutting or grinding by a rotary
instrument.
FINISHING: Process of removing surface defects/scratches.
POLISHING: Polishing is the process of providing luster or gloss on a material surface.
FINISHED & POLISHED RESTORATION: A prosthesis or a direct restoration whose outer surface has
been refined to a desired state of finish.

GRINDING
Is the process of
removing material by
abrasion with relatively
coarse particles.
CONTOURING
Is the process of
producing a desired
anatomical form by
cutting or grinding.

Factors Affecting Rate of Abrasion
The following factors causes changes in the rate of abrasion of an abrasive:
 HARDNESS: Hardness of an abrasive is directly proportional to the rate of its abrasion i.e. the harder the
abrasive than the substrate the more abrasion will be produced.
 PARTICLE SIZE: The particle size of a material is
Expressed in MICROMETRES.
By convention, particles are classified as
 FINE 0 - 10µm
 MEDIUM 10 - 100µm
 COARSE 100 - 1000µm
Larger, coarse abrasive particles will abrade a surface more readily than smaller particles, but they
tend to leave more coarser scratches in the substrate.
PARTICLE SHAPE: Sharp, irregular shaped particles will abrade a surface more rapidly than will rounded
particles having dull cutting angles. However the former will produce deeper scratches than later.
SPEED & PRESSURE: Both speed & pressure are directly proportional to the rate of abrasion.
 At higher speed greater friction is produced, which tends to produce higher temperatures.
 Similarly, greater pressure causes higher temperatures & possibly patient discomfort.
 LUBRICATION: Lubricants are used during abrasion for two purposes:
 to reduce heat buildup
 to wash away debris to prevent clogging
but too much lubrication can reduce the abrasion rate by preventing the abrasive from coming in contact
with the substrate.

Some factors which will affect how quickly a substance is abraded include:
 Difference in hardness between the two substances: a much harder abrasive will
cut faster and deeper
 Grain size: larger grains will cut faster as they also cut deeper
 Adhesion between grains, between grains and backing, between grains and
matrix: determines how quickly grains are lost from the abrasive and how soon fresh
grains, if present, are exposed
 Contact force: more force will cause faster abrasion
 Loading: worn abrasive and cast off work material tends to fill spaces between
abrasive grains so reducing cutting efficiency while increasing friction
 Use of lubricant/coolant/metalworking fluid: Can carry away swarf (preventing
loading), transport heat (which may affect the physical properties of the workpiece or
the abrasive), decrease friction (with the substrate or matrix), suspend worn work
material and abrasives allowing for a finer finish, conduct stress to the workpiece.

Good Abrasive
 They are cheap
 They last a long time
 They cut or wear surfaces that you want cut or
worn quickly
 They don’t cut things you don’t want them to
 Hardness is an obvious important factor
 Size and shape also are important

 DIAMOND
is a transparent, colorless mineral composed of carbon. It is the hardest
known substance & is called a super abrasive because of its ability to abrade
any other known substance.
 Hardness of the diamond is unmatched and for many applications they are
irreplaceable for cutting
 Industrial diamonds lack the color and perfection of jewlery
 Major uses
 Diamond bits for rock and concrete
 Diamond dies for wire drawing
 Diamond tipped tools and wheels
Nature Abrasive Minerals
 Many minerals and rocks of diverse composition but with one thing in
common “Hardness”.
 are used in the natural state, except for processing and bonding.
 Are being supplanted by artificial abrasives.

 Synthetic diamond
abrasives
are used far more commonly
than natural diamond due to its
consistent shape & size & low
cost.
Diamonds are mostly used on
ceramics & resin-based composite
materials.
C
Specific Gravity: 3.5 - 3.53
Hardness :10
Color: Colourless,
yellowish to yellow, brown,
black, blue, green or red,
pink, champagne-tan,
cognac-brown, lilac (very
rare)

Corundum/ Emery
 Lots of gems are corundum
 Much of abrasive market has been taken by synthetic
minerals
 Get more uniform material without random natural
weaknesses
 Still used for super heavy duty concrete and
durable anti-skid material
Al2O3
S.G. 3.98 - 4.1
Hardness 9
Color Colourless, blue, red, pink, yellow, grey,
golden-brown
Gem forms include Rubies and Sapphires, Emery
Where Corundum is Found

EMERY
is a mixtute of fine-
grain grayish black
corundum, magnetite,
and some hematite
and spinel.
 used for finishing and
polishing metals; Glass
grinding
CORUNDUM
is a white mineral form of Al2O3.
It is used primarily for grinding metal
alloys.

Zircon
(or Zirconium
silicate)
is an off-white mineral.
It is frequently used as a
component of dental
prophylactic pastes.

 GARNET
consists of a group of different minerals that have the same physical properties &
crystalline forms. Minerals included in this group are silicates of Al, Co, Fe, Mg & Mn. The type of
garnet used in dentistry is usually dark red. It is used in grinding metal alloys & acrylic resin materials.
 Use as a grinding and polishing agent:
 Garnet papers still common abrasive
 Also used as a “sand blasting agent”
 It does not cause silicosis
 Filtering material
 A lot of natural sharpening rocks in fact get their properties from well distributed small garnet
crystals.
World Wide Garnet Mine Locations

Common Nesosilicates: Garnet
(Mg,Fe,Mn,Ca)3(Fe3+,Cr,Al)2Si3O12
As mod-T metamorphic mineral formed from Al-rich source rocks
and ultramafic mantle rocks (eclogites)
Equigranular, euhderal to subhedral habit; poor cleavage
Optics: Colorless, isotropic, high relief (n~1.7-1.9)
Complex solid solution with the following end-member
compositions and their characteristic colors:
Pyrope Mg3Al2Si3O12 – deep red to black; S.G. 3.5 - 3.6;
Hardness 7.5
Almandine Fe3Al2Si3O12 – deep brownish red; S.G. 4.09 - 4.31,
Average = 4.19; Hardness 7-8
Spessartine Mn3Al2Si3O12 – brownish red to black
Grossular Ca3Al2Si3O12 – yellow-green to brown; S.G. 3.42 -
3.72, Average = 3.57 ; Hardness 6.5-7.5
Andradite Ca3Fe2Si3O12 – variable-yellow, green, brown, black;
S.G. 3.8 - 3.9; Hardness 6½ - 7½
Uvarovite Ca3Cr2Si3O12 – emerald green
Almandine
Grossular
Andradite

Garnet A3B2Si3O12
Usually B is Aluminum, A divalent
Almandine Fe3Al2Si3O8
B-site
Aluminum
octahedral
A-site Fe++,
Mg++, Ca++,
Mn++ in
distorted
octahedra

• Garnet Group (X3Y2 {SiO4}3)
 X{A} –> divalent cations: Ca+2, Mn+2, Fe+2, Mg+2
 Y{B} –> trivalent cations: Al+3, Fe+3, Cr+3
 Generally high-grade (high temp and/or pressure)
metamorphic rock occurrence
 Gem stone of high hardness: 7-7.5
Nesosilicates: Garnet Group

Almandite
Fe3Al2(SiO4)3
S.G. 4.09 - 4.31, Average = 4.19; Hardness 7-8
Color Brown, Brownish red, Red, Black,
Black red.
Fluorescence None
Ca3Al2(SiO4)3
S.G. 3.42 - 3.72, Average = 3.57
Hardness 6.5-7.5
Color Brown, Colorless, Green,
Gray, Yellow.
Fluorescence None
Grossularite
Andradite Ca3Fe2(SiO4)3
S.G. 3.8 - 3.9;
Hardness 6½ - 7½
Color Green, yellow,
orange, reddish-
brown,
brown, black
Fluorescence not
reported
Pyrope
Mg3Al2[SiO4]3
S.G. 3.5 - 3.6; Hardness 7.5
Color Blood red, orange red,
purple red, pink, or black red
Fluorescence not reported

Staurolite
 Industrial application is as a “Sand Blasting Agent”
 Also used as a gemstone
(Fe,Mg)2Al9(Si,Al)4O20(O,OH)4
S.G. 3.65 - 3.77, Average = 3.71
Hardness 7-7.5
Color Brownish yellow,
Brownish black, Yellow brown,
Dark brown, Reddish brown.

Silica
What is Silica?
 “Crystalline Silica” and “Quartz” refer to the same thing
 2nd most common mineral in the earth’s crust
 Major component of sand, rock, granite and mineral ore
 Toxic and less/nontoxic form
 Sand is still dominant material for “Sand Blasting”
 Carefully graded and sized sand is used for “flint”
sandpapers
Dominant market is home use
 Fine pure sands are an important raw material for glass,
ceramics, and synthetic abrasives
 Naturally fine almost amorphous material that breaks
up easily is called Tripoli

Types of Silica
TOXIC
Silica, Crystalline (as dust)
Trade Names
Cristobalite
Tridymite
Tripoli
Quartz
Common-Sandblasters
NON/LESS TOXIC
Silica, Amorphous
Trade Names
Diatomaceous earth
Diatomaceous silica
Diatomite
Silica Gel
Silicon Dioxide
(amorphous)

 QUARTZ
is a hard, colorless,
transparent & most
abundant mineral. It is
used mainly to finish
metal alloys.
 SAND
is a mixture of mineral particles,
predominantly composed of silica. The
particles represent a mixture of colors,
making it distinct in appearance. They
are coated onto paper disks for
grinding of metals. (Sandpaper and
sandblasting)
SiO2
S.G. 2.6 - 2.65, Average = 2.62
Hardness 7
Color Brown, Colorless, Violet, Gray,
Yellow.

 TRIPOLI
is derived from a light-
weight, friable siliceous
sedimentary rock. Tripoli
can be white, gray, pink,
red or yellow.
It is used for soft abrasive,
buffing blocks and
powders
SiO2
S.G. 2.7
Hardness 7
Color
White, buff
Fluorescence
None
Magnetic- No

Soft Scrubbing Powders
Diatomite
Used in silver polishes
More common use is filtering media
Pumice
Main ingrediant in polishing powders and
household cleaners
Including tooth paste
Used in hard rubbers
Used for washing stones for blue jeans

 KIESELGUHR
is composed of the
remains of minute aquatic
plants known as diatoms.
Its coarser form is called
diatomaceous earth & is
used as a filler in many
dental materials, such as
hydrocolloid impression
materials.
 CUTTLE
commonly referred
to as cuttlefish or cuttle
bone, is a white
calcareous powder made
from the internal shell of a
Mediterranean marine
mollusk.
It is available as coated
abrasive & used for
polishing metal margins.

 PUMICE
is a light gray volcanic rock
derivative, used in polishing
tooth enamel, gold foil, dental
amalgam & acrylic resins.
• Pumice is about 60-70% silica
• It has no crystal structure – it is
a frothy glass
• S.G. < 1

Other Soft Abrasives
Ground Feldspar in window cleaners
Chalk for fine soft metal polishes
Kaolin
 CHALK
Is a white
abrasive composed of
CaCO3. Chalk is used
as a mild abrasive
paste to polish tooth
enamel, gold foil,
amalgam & plastic
materials.

Synthetic Abrasive
SILICON CARBIDE (SiC)
It was the first of the synthetic abrasives to be produced. It is
available in green & blue-black types, having equivalent physical properties.
Silicon carbide is extremely hard (Its hardness is 13 mohos
,
scale) & brittle
& results in highly efficient cutting of materials, including metal alloys,
ceramics & acrylic resins
It is available as an abrasive in coated discs, & bonded instruments.
.

 ALUMINUM OXIDE (Al2O3)
Fused aluminum oxide was the second synthetic abrasive to be developed.
 Fused alumina is trade names of Alundum and Aloxite.
 Is made of bauxite fused in an electric furnace with coke and iron for 24 hours at
1000oC.
 Aluminum oxide (alumina) is much harder than corundum due to its purity.
 Several grain sizes are available & has largely replaced emery for several abrasive
uses.
 Alumina is used in the form of vitrified wheels and powders & for finishing metal
alloys, resin-based composites & ceramic materials.

 ROUGE
Fe2O3 is the fine, red abrasive
component of rouge.
Like tripoli, rouge is blended with various
soft binders into a cake form.
It is used to polish high noble metal alloys.
 TIN OXIDE
SnO is an extremely
fine abrasive used
extensively as a polishing
agent for polishing teeth
& metallic restorations.
It is mixed with water,
alcohol or glycerin to form
a mildly abrasive pastes.

 ABRASIVE PASTES
The most commonly used abrasive pastes
contain either alumina or diamond particles.
Alumina pastes should be used with a rotary
instrument & increasing amounts of water.
Diamond abrasive pastes are used in dry
conditions.
Abrasive pastes have several disadvantages like:
 they are relatively thick & so don’t readily gain
access to embrasures.
 they tend to splatter off of the instruments.
 heat is generated when insufficient coolant is
used or when an intermittent polishing
technique is not used.

What is Abrasive Blasting?
 Operations where an abrasive is forcibly applied to a surface by
pneumatic or hydraulic pressure or by centrifugal force.
 Does not apply to steam blasting or steam cleaning or hydraulic-
cleaning methods where work is done without the aid of abrasives
 Frequently used for:
 cleaning sand from foundry castings
 cleaning and removing paint from metal surfaces
 finishing tombstones
 etching and frosting glass
Surface Preparation
With Garnet Abrasive

Thomps
on Valve
Thompson
Valve II
MicroValve
Metering of Garnet Abrasive
Reduce Air Emissions
with Garnet Blast
Blasting with slag

Abrasive and Abrasion Minerals

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Abrasive and Abrasion Minerals