Defining basalt and sandstone by devagya gandhi only.

1. DEFINING
BASALT AND
SANDSTONE
MADE BY DEVAGYA GANDHI OF
CLASS 4-B OF SECOND YEAR

2. INTRODUCTION:
The history of mankind is supposed to have begun with the stone age marked by the use of
implements and weapons made of stone. Prior to that, the difference between animals and
homosapiens was largely physical. But once human beings started using stones, the world of
both changed entirely.
Stone has been defined as the natural, hard substance formed from minerals and earth
material which are present in rocks. Rock may be defined as the portion of the earth’s crust
having no definite shape and structure. Almost all rocks have a definite chemical composition
and are made up of minerals and organic matter. Some of the rock-forming minerals are quartz,
felspar, mica, dolomite, etc. The various types of rocks from which building stones are usually
derived are granite, basalt, trap, marble, slate, sandstone and limestone.
Use of stone in building construction is traditional in the places where it is produced,
although even there its high cost imposes limitations on its use. The conditions which govern
the selection of stone for structural purposes are cost, fashion, ornamental value and
durability.
Stone has been used in the construction of most of the important structures since prehistoric
age. Most of the forts world over, the Taj Mahal of India, the famous pyramids of Egypt and
the
great wall of China are but a few examples. Stone has also been extensively used in almost all
the elements of building structures, as load carrying units as well as for enhancing the beauty
and elegance of the structure. As building material stone has gradually lost importance with
the advent of cement and steel. Secondly, the strength of the structural elements built with
stones cannot be rationally
analysed. Other major factors in
overshadowing its use are the
difficulties in its transportation
and dressing which consume a lot
of time resulting in slow
pace of construction.

3. SANDSTONE:
Sandstone is a sedimentary rock and one of the most common types of sedimentary rock and is found in
sedimentary basins throughout the world. It is composed of sand-size grains rock fragment, mineral and
organic material. Sand-size particles range in size from 1/16 millimeter to 2 millimeters in diameter. Also it
have cementing material binds the sand grains together and may contain a matrix of silt- or clay-size
particles that occupy the spaces between the sand grains.Quartz-bearing sandstone can be changed into
quartzite through metamorphism, usually related to tectonic compression within orogenic belts.
Texture: Clastic (only noticeable with a microscope).Grain size: 0.06 – 2mm; clasts visible to the naked eye,
often identifiable.Hardness: Variable, soft to hard, dependent on clast and cement composition.Colour:
Variable through grey, yellow, red to white reflecting the variation in mineral content and cement.Clasts:
Dominantly quartz and feldspar ( orthoclase, plagioclase) with lithic clasts and varying minor amounts of
other minerals.
Other features: Gritty to touch (like sandpaper).Minerals: Quartz or feldspar (both silicates)
Sandstone Composition
Chemical Composition of sandstone usually quartz framework grains are the dominant mineral in clastic
sedimentary rocks. Because of they have exceptional physical properties such as hardness and chemical
stability.Physcial properties of these quartz grains survive multiple recycling events and also allowing the
grains to display some degree of rounding. Quartz grains evolve from plutonic rock, which are felsic in
origin and also from older sandstones that have been recycled. Second most abundant mineral is feldspathic
framework grains.Feldspar can be seperate into two subdibision. They are alkali feldspars and plagioclase
feldspars. Feldspars minerals is distinguished under a petrographic microscope.Alkali feldspar is a group of
minerals in which the chemical composition of the mineral can range from KAlSi3O8 to NaAlSi3O8, this
represents a complete solid solution.Plagioclase feldspar is a complex group of solid solution minerals that
range in composition from NaAlSi3O8 to CaAl2Si2O8.
Photomicrograph of a volcanic sand grain; upper picture is plane-polarised light, bottom picture is cross-
polarised light, scale box at left-centre is 0.25 millimetre. This type of grain would be a main component of
a lithic sandstone.Lithic framework grains are pieces of ancient source rock that have yet to weather away
to individual mineral grains, called lithic fragments or clasts. Lithic fragments can be any fine-grained or
coarse-grained igneous, metamorphic, or sedimentary rock, although the most common lithic fragments
found in sedimentary rocks are clasts of volcanic rocks.
Accessory minerals are small percentage of the grain in a sandstone.Common accessory minerals include
micas (muscovite and biotite), olivine, pyroxene, and corundum. Many of these accessory grains are more
density to silicates minerals in the rocks. These heavy minerals moere durability to weathering and can be
used as an indicator of sandstone maturity through the ZTR index.
Common heavy minerals include zircon, tourmaline, rutile (hence ZTR), garnet, magnetite, or other dense,
resistant minerals derived from the source rock.

4. Matrix:Matrix is present within fractured pore space between the framework grains. This pore space can be seperate
into the two class. They are Arenites and Wackes. Arenites are texturally clean sandstones that are free of or have
very little matrix. Wackes are texturally dirty sandstones that have a significant amount of matrix.
Cement:Cement is binds the siliciclastic framework grains together. Cement is a secondary deposition minerals after
during burial of sandstone.These cementing materials may be either silicate minerals or non-silicate minerals, such as
calcite. Silica cement can consist of either quartz or opal minerals. Calcite cement is the most common carbonate
cement. Calcite cement is an assortment of smaller calcite crystals. Other minerals that act as cements include:
hematite, limonite, feldspars, anhydrite, gypsum, barite, clay minerals, and zeolite minerals.
Sandstone Formation
Formation of the sandstones are cemented grains that may either be fragments of a pre-existing rock or be mono-
minerallic crystals. The cements binding these grains together are typically calcite, clays, and silica. Grain sizes in
sands are defined (in geology) within the range of 0.0625 mm to 2 mm (0.0025–0.08 inches). Clays and sediments
with smaller grain sizes not visible with the naked eye, including siltstones and shales, are typically called
argillaceous sediments; rocks with larger grain sizes, including breccias and conglomerates, are termed rudaceous
sediments. The most common cementing materials are silica and calcium carbonate, which are often derived either
from dissolution or from alteration of the sand after it was buried. Colors will usually be tan or yellow (from a blend
of the clear quartz with the dark amber feldspar content of the sand). The environment where it is deposited is
crucial in determining the characteristics of the resulting sandstone, which, in finer detail, include its grain size,
sorting, and composition and, in more general detail, include the rock geometry and sedimentary structures.
Principal environments of deposition may be split between terrestrial and marine, as illustrated by the following
broad groupings:
Terrestrial environments
Rivers (levees, point bars, channel sands)
Alluvial fans
Glacial outwash
Lakes
Deserts (sand dunes and ergs)
Where is the Sandstone found?
Sandstone can be found to many place to deposits across the World. In the USA, there are four main sandstone
deposits that can be found in Virginia, Wisconsin, Michigan and New York. Aquia Creek Sandstone, found in Stafford
County Virginia, has been used in many of Washington’s prominent government buildings, including the White
House. There are at least 8 varieties of sandstone to be found in South Africa, but many of the quarries in this
country have since closed down. Europe is home to most of the sandstone deposits of the world, with countries such
as Switzerland, Germany and France holding the bulk of them. Germany, in fact, lays claim on having the most
deposits in the entire world with around 64 varieties of the stone all being found in different areas.
Sandstone Uses
Sandstone was used domestic construction and housewares even in prehistoric times.
Sandstone was a popular building material from ancient times. It is relatively soft, making it easy to carve. It has been
widely used around the world in constructing temples, homes, and other buildings.
It has also been used for artistic purposes to create ornamental fountains and statues.
Some sandstones are resistant to weathering, yet are easy to work. This makes sandstone a common building and
paving material including in asphalt concrete.
Because of the hardness of individual grains, uniformity of grain size and friability of their structure, some types of
sandstone are excellent materials from which to make grindstones, for sharpening blades and other implements.
Conclusion
Sandstone is a versatile building structure and has been used to construct buildings, statues, and fountains.
Sandstone is popular in constructing buildings because it is resistant to weathering.
Sandstone can form under the sea or on land.
It is common to find natural gas in sandstone because sandstone is porous and traps it.
Grindstone wheels, which are used for sharpening, are made of sandstone.
Sandstone can be categorized into three groups: arkosic, quartzose, and argillaceous.
Because sandstone is porous it can serve as a filter in nature by filtering out pollutants from running water.
Sandstone is often broken down and used as industrial sand.
Groundwater can be transported by underground sandstone.
Underground sandstone is drilled and pumped as a good source for groundwater.
Sandstone rock can take thousands of years to form.

5. BASALT STONE
Basalt
Basalt is a very common dark-colored volcanic rock composed of calcic plagioclase
(usually labradorite), clinopyroxene (augite) and iron ore (titaniferous magnetite).
Basalt may also contain olivine, quartz, hornblende, nepheline, orthopyroxene,
etc. Basalt is a volcanic equivalent of gabbro.Basalt is usually black or dark gray
and relatively featureless. It is composed of mineral grains which are mostly
indistinguishable to the naked eye. Basalt may also contain volcanic glass. Basalt
may contain phenocrysts (larger crystals within fine-grained groundmass) and
vesicules (holes that were filled by volcanic gases).
Black color is given to basalt by pyroxene and magnetite. Both of them contain
iron and this is the reason why they are black. So this is iron again which is
responsible for the coloration of basalt. Plagioclase, volumetrically usually the
most important constituent, is mostly pale gray in color.
Basalt is a major rock type that occurs in virtually every tectonic setting. Basalt is
clearly the most common volcanic rock on Earth and basaltic rocks (including
gabbro, diabase and their metamorphosed equivalents) are the most common
rocks in the crust2. Basalt is also common on the Moon and other rocky planets of
the Solar System.
What makes basalt so common? Basalt is the original constituent of the crust from
which almost all other rock types have evolved. Basalt forms when mantle rocks
(peridotite) start to melt. Rocks melt incongruently. It basically means that melt that
forms has a different composition from the source rocks. Of course, it can only
happen if rocks melt only partially, but this is exactly what happens in the upper
mantle. It melts partially to yield basaltic magma which is less dense and rises
upward to form new oceanic crust in mid-ocean ridges or volcanoes and intrusives
(dikes, sills) in many other tectonic regimes. Basalt is the source rock of other more
evolved volcanic rocks like dacite, rhyolite, etc.

6. CLASSIFICATION
Basalt has a strict chemical definition. It is defined in the TAS diagram shown above. Basalt is an igneous rock that contains
more than 45 and less than 52% of SiO2 and less than five percent of total alkalies (K2O + Na2O)3.
'
Neighboring rock types like basaltic andesite, basanite, picrite (picrobasalt), trachybasalt and even more distant rocks like
phonotephrite or andesite may have very similar look and can be easily mistaken for basalt in many cases.
Basalt is widespread in many tectonic regimes, but there are slight variations in chemical composition which allow more
precise classification. MORB is an acronym for “mid-ocean ridge basalt” and OIB for “oceanic island basalt”. MORB is a result
of partial melting of the upper mantle which is already recycled many times while OIB is at least partly from more deeper part
of the mantle (deep-sourced mantle plumes that feed hot spots like Hawai’i or the Canary Islands) and is therefore less
depleted in incompatible chemical elements.
Andesite is similar to basalt, but it contains more silica and is generally lighter in color. White crystals are plagioclase
phenocrysts, but they contain less Ca and more Na than plagioclase in basalt does. Andesite is very common product of
subduction zone volcanism. Santorini, Greece. Width of sample 7 cm.
Composition
Average chemical composition of basalt determined by 3594 chemical analyses of basaltic rocks2 (numbers are mass
percents, recalculated volatile-free to total 100%):
SiO2 — 49.97
TiO2 — 1.87
Al2O3 — 15.99
Fe2O3 — 3.85
FeO — 7.24
MnO — 0.20
MgO — 6.84
CaO — 9.62
Na2O — 2.96
K2O — 1.12
P2O5 — 0.35
'
Minerals that host these chemical elements (chemical composition of igneous rocks is traditionally expressed in oxides) are
augite, plagioclase and titaniferous magnetite. These minerals are difficult to demonstrate because they are too small to be
seen in typical basalt, but some basaltic rocks are porphyritic (lots of porphyritic rocks can be seen here: porphyry) and show
some of these minerals nicely (unfortunately not magnetite, though).
Basalt porphyrite from the Isle of Mull, Scotland with many plagioclase phenocrysts. The rock is 8 cm in length.
Porphyritic basaltic rock from Tenerife. Phenocrysts are plagioclase (white) and augite (black). Width of sample 14 cm.
Magnetite crystals are always microscopic in basalt, but sometimes they form black stripes in light-colored sand. Here are
heavy minerals (mostly magnetite) as a residue of weathering of basaltic rocks. White Park Bay, Northern Ireland.
Basaltic rock (most likely basanite) from Caldera de Taburiente, La Palma. Black is pyroxene augite, orange is olivine or more
precisely what is left of it. Orange patches are former olivine crystals that are now composed of a mixture of silicates and iron
oxides which is known as iddingsite. Olivine is a common mineral in many basaltic rocks. Width of view 10 cm.
Another basalt (chemically probably picrobasalt) with lots of olivine (fresh olivine is bright green, but it gets more and more
yellow as it weathers). Oahu, Hawai’i. Width of sample 6 cm.

7. Metamorphism and weathering
Basalt is largely composed of minerals with little resistance to weathering. Hence,
basalt as a whole also tends to disintegrate faster than granite and other felsic
rock types. Magnetite is one of the most resistant common minerals in basalt and
forms the bulk of heavy mineral sands. Other minerals disintegrate and release
their components to water as ions or form clay minerals. Iron and aluminum are
among the least mobile ions and therefore tend to form laterite deposits enriched
in these elements.
Basalt metamorphoses to a number of different rock types, depending on
pressure, temperature, and the nature of volatile compounds that react with
minerals in basalt. Most common metamorphic rocks with basaltic protolith are
chlorite schist, amphibolite, blueschist, and eclogite.
'
Black sand forms in volcanic islands when quartz and biogenic grains are not
available. Here is a basaltic cliff and black sand on La Palma, Canary Islands.
Chlorite schist is a low-grade metamorphosed mafic igneous rock, often with a
basaltic protolith. Iron-bearing green sheet silicate mineral chlorite gives slaty
cleavage to the rock. Width of sample 13 cm.
Etymology
The term “basanite” was already used in antiquity and “basalt” is probably a
faulty transcription of basanite. It was German scholar Agricola (Georg Bauer)
who first mentioned “basalt” in 1546. He referred to black columnar rocks from
Stolpen (near Dresden in Germany) which is indeed basalt even according to
modern classification principles.

8. THE END