Garnet GROUP OF MINERAL

1. DR. HARISINGH GOUR
VISHWAVIDYALAYA
SAGAR, M.P
(CENTRAL UNIVERSITY)
DEPARTMENT OF APPLIED GEOLOGY
GARNET GROUP
Under guidance of: Presented by:
Dr. G.C.Gautam Abhishek Chaurasiya
Y18251001
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2. CONTENT
 Introduction
 Chemical composition of garnet
 Structure
 Classification
 Physical properties
 Optical properties
 Occurrence
 Gem variety
 Uses
 conclusion
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3. INTRODUCTION
Garnet is a group of six minerals which are
isomorphous in nature and never occur pure as
represented by their chemical composition.
It is a hard silicate mineral which occurs in
many rocks but it is especially common in some
metamorphic rock like schist.
The garnets vary only slightly in physical
properties and some of the minerals may be so
similar that they are indistinguishable from one
another without a X-ray analysis.
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4. CHEMICAL COMPOSITION
General formula: X3 Y2(SiO4)3
Where,
X - Ca, Mg, Fe, Mn
Y – Fe, Al, Cr
Pyrope - Mg3Al2(sio4)3
Almandine - Fe3Al2(SiO4)3
Spessartine – Mn3Al2(SiO4)3
Uvarovite - Ca3Cr2(SiO4)3
Grossularite – Ca3Al2(SiO4)3
Andradite - Ca3Fe2(SiO4)3
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5. 5
Garnets consist of groups of independent,
distorted SiO4tetrahedrons, each of which is
linked, by sharing corners, to
distorted BO6 (e.g., aluminum- and/or iron-
centred) octahedrons, thus forming a three-
dimensional framework
The interstices are occupied by A
divalent metal ions (e.g., Ca, Fe2+
, Mg,
and Mn), so that each one is
surrounded by eight oxygen atoms that
are at the corners of a distorted cube.
Therefore, each oxygen is coordinated
by two A, one B,and one silicon cation
The configuration of the array is such
that garnets are isometric (cubic).
STRUCTURE

6. 6
Garnets commonly occur as well developed crystal .The typical form of
the crystals have 12 or 24 sides and are called dodecahedron and
trapezohedron respectively.Crystal habits can be co-related with
chemical composition i.e. dodecahedron are most likely to be grossular
rich ,trapezohedron tend to be pyrope,almandine or spessartine and
combination of dodecahedron and trapezohedron are generally
andradite rich.

7. CLASSIFICATION
Mainly there are two series:
1) Pyralpsite
a) Pyrope - Mg3Al2(SiO4)3
b) Almandine - Fe3Al2(SiO4)3
c) Spessartine – Mn3Al2(SiO4)3
2) Ugrandite
a) Uvarovite - Ca3Cr2(SiO4)3
b) Grossularite – Ca3Al2(SiO4)3
c) Andradite - Ca3Fe2(SiO4)3 7

8. 8
(a) (b)
IN THE GIVEN FIGURE MINERAL COMPOSITIONS IN THE
GARNET GROUP SHADED AREAS INDICATES
COMPOSITIONAL REGIONS FOR NATURAL
GARNETS,UNSHADED REGION INDICATES
COMPOSITIONAL REGION UNREPRESENTED BY
NATURAL GARNETS

9. PHYSICAL PROPERTIES
1) Colour : Red, brown, black, green,yellow
orange, pink, white
2) Streak: colourless
3) Luster: Resinous, dull, vitreous
4) Cleavage : absent
5) Fracture : conchoidal to uneven
6) Hardness : 7
7) Specific gravity : high
8) Transparency: Transparent to translucent
9) Habit : Euhedral to Subhedral
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10. OPTICAL PROPERTIES OF GARNET
UNDER PLANE POLARISED
LIGHT
UNDER CROSSED NICOL
COLOUR – Pale pink
FORM - Euhedral to subhedral
RELIEF - High
CLEAVAGE – Absent
FRACTURE – Present
PLEOCHROISM - Absent
ISOTROPIC
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11. OCCURENCES
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GEM VARIETY OF GARNET
Garnet’s color,hardness and transparency make them attractive stone for use
as a gemstone .
six main garnet minerals are
almandine
Pyrope
spessartine
Grossular
Andradite
Uvarovite
More general garnet gem variety
Demantoid-olive green to emerald green gem variety of andradite garnet
Hessonite-orange to orange brown,transparent variety of grossular garnet
Imperial garnet-light pink,transparent varietyof grossular garnet
Malaya garnet – reddish orange form of spessartine
Rhodolite- rose red form of garnet with light color . It is intermediate variety of
pyrope and almandine

13. 13
Rhodolite- rose red form of garnet with light color . It is
intermediate variety of pyrope and almandine
Melanite- lustrous, opaqe black or very dark red variety of
andradite
Topazolite- yellow to brownish yellow variety of andradite
garnet
Tsavorite – green to emerald green transparent variety of
grossular garnet

14. GARNETS
ALMANDINE PYROPE
GROSSULARUVAROVITEANDRADITE
SPESSARTINE
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15. USES OF GARNET
Garnet Abrasives -The first industrial use of garnet
was as an abrasive. That allows it to be used as an
effective abrasive in many types of manufacturing.
Water jet Cutting - A machine known as a water
jet cutter produces a high-pressure jet of water
with entrained abrasive granules of garnet
which is used in cutting metals, stones etc.
Abrasive Blasting- Garnet granules are also
used in abrasive blasting to smooth, clean, or to
remove oxidation products from metals, brick,
stone, and other materials.
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16. Filtration -Garnet granules are often used as a filter
media. Small garnet particles are used to fill a container
through which a liquid flows.
Gemstone - Garnet is used as gemstones due to its wide
variety of colours, lustre and hardness.
Garnet as a Geological Indicator Mineral- It is an
indicator mineral for prospecting diamond.
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17. USES OF GARNET
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18. CONCLUSION
 Garnet group of minerals is one of the important
group of minerals.
 Since they are found in wide variety of colours,
they are also used as gemstones.
 Garnet group of minerals are also abrasives and
thus have various industrial applications.
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19. REFERENCES
 Dana, Textbook of mineralogy,4th
edition, CBS
Publishers, 591p
 Perkins Dexter, Mineralogy, 3rd
edition, PHI Learning
Private Limited, 338p
 Karr P.F, Mineral optics, 353p
 www.googlesearch.com
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20. THANK YOU
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