NAME
Basalt
DESCRIPTION
Basalt is a dark-coloured, fine-grained, igneous rock
composed mainly of plagioclase and pyroxene minerals. It
most commonly forms as an extrusive rock, such as a
lava flow, but can also form in small intrusive bodies, such
as an igneous dike or a thin sill. It has a composition
similar to gabbro. The difference between basalt and
gabbro is that basalt is a fine-grained rock while gabbro is
a coarse-grained rock.
Gabbro is a coarse-grained, dark-coloured, intrusive
igneous rock. It is usually black or dark green in colour
and composed mainly of the minerals plagioclase and
augite. It is the most abundant rock in the deep oceanic
crust.
Gabbro
Pumice
Pumice is a volcanic rock that consists of highly vesicular
volcanic glass, which may or may not contain crystals. It is
typically light coloured. Pumice is created when superheated, highly pressurized rock is violently ejected from a
volcano. The unusual foamy configuration of pumice
happens because of simultaneous rapid cooling and rapid
depressurization. The depressurization creates bubbles
by lowering the solubility of gases (including water and
CO2) that are dissolved in the lava, causing the gases to
rapidly exsolve (like the bubbles of CO2 that appear when
a carbonated drink is opened). The simultaneous cooling
and depressurization freezes the bubbles in the matrix.
Obsidian is an igneous rock that forms when molten rock
material cools so rapidly that atoms are unable to arrange
themselves into a crystalline structure. The result is a
volcanic glass with a smooth uniform texture that breaks
with a conchoidal fracture.
Obsidian
Dacite
Dacite is an extrusive igneous rock. Dacite lava is most
often light gray, but can be dark gray to black. Dacite lava
consists of about 63 to 68 percent silica (SiO2). The
principle minerals that make up dacite are plagioclase,
quartz, pyroxene, or hornblende. Dacite generally erupts
at temperatures between 800 and 1000 degrees C., and
is one of the most common rock types associated with
enormous Plinian-style eruptions.
"Snowflake" obsidian is a shiny black, glass-like stone
with gray and white markings. These lighter colored
splotches appear like beautiful patterns of snowflakes
against a striking black background.
Snowflake
Obsidian
The term "Snowflake" obsidian comes from the
combination of cristobalite nodules in obsidian. The
cristobalite spots are called spherulites.
PICTURE
Granite
Marble
Slate
Gneiss
Quartzite
Coal
Granite is a common widely occurring type of intrusive,
felsic, igneous rock which is granular and crystalline in
texture. This rock consists mainly of quartz, mica, and
feldspar.
Occasionally
some
individual
crystals
(phenocrysts) are larger than the groundmass, in which
case the texture is known as porphyritic. A granitic rock
with a porphyritic texture is sometimes known as a
porphyry. Granites can be pink to grey in colour,
depending on their chemistry and mineralogy.
Marble is a non-foliated metamorphic rock composed of
recrystallized carbonate minerals, most commonly calcite
or dolomite. Geologists use the term "marble" to refer to
metamorphosed limestone; however stonemasons use
the term more broadly to encompass unmetamorphosed
limestone.
Slate is a fine-grained, foliated metamorphic rock that is
created by the alteration of shale or mudstone by lowgrade regional metamorphism. Slate is composed mainly
of clay minerals or micas depending upon the degree of
metamorphism to which it has been subjected. The
original clay minerals in shale alter to micas with
increasing levels of heat and pressure. Slate can also
contain abundant quartz and small amounts of feldspar,
calcite, pyrite, hematite and other minerals. Most slates
are grey in colour and range in a continuum of shades
from light to dark grey. Slate also occurs in shades of
green, red, black, purple and brown. The colour of slate is
often determined by the amount and type of iron and
organic material that are present in the rock.
Gneiss is foliated metamorphic rock that has a banded
appearance and is made up of granular mineral grains. It
typically contains abundant quartz or feldspar minerals.
These rocks may have been granite, which is an igneous
rock, but heat and pressure changed it. You can see how
the mineral grains in the rock were flattened through
tremendous heat and pressure and are arranged in
alternating patterns.
Quartzite is a non-foliated metamorphic rock that is
produced by the metamorphism of sandstone. It is
composed primarily of quartz. Pure quartzite is usually
white to grey, though quartzites often occur in various
shades of pink and red due to varying amounts of iron
oxide (Fe2O3). Other colours, such as yellow and orange,
are due to other mineral impurities.
Coal is an organic sedimentary rock that forms from the
accumulation and preservation of plant materials, usually
in a swamp environment. Coal is a combustible rock and
along with oil and natural gas it is one of the three most
important fossil fuels. Coal has a wide range of uses; the
most important use is for the generation of electricity.
Conglomerate
Breccia
Limestone
Red
Sandstone
Conglomerate is a clastic sedimentary rock that contains
large (greater than two millimetres in diameter) rounded
clasts. The space between the clasts is generally filled
with smaller particles and/or a chemical cement that binds
the rock together.
Breccia is a term most often used for clastic sedimentary
rocks that are composed of large angular fragments (over
two millimetres in diameter). The spaces between the
large angular fragments can be filled with a matrix of
smaller particles or a mineral cement that binds the rock
together. Breccia can be any colour. The colour of the
matrix or cement along with the colour of the angular rock
fragments determine its colour.
Limestone is a sedimentary rock composed primarily of
calcium carbonate (CaCO3) in the form of the mineral
calcite. It most commonly forms in clear, warm, shallow
marine waters. It is usually an organic sedimentary rock
that forms from the accumulation of shell, coral, algal and
fecal debris. It can also be a chemical sedimentary rock
formed by the precipitation of calcium carbonate from lake
or ocean water.
Sandstone is a category of rock made from sediment (a
sedimentary rock). The sediment particles are clasts, or
pieces, of minerals and fragments of rock, thus sandstone
is a clastic sedimentary rock. It is composed mostly of
sand, which means particles of a medium size, so
sandstone is a medium-grained clastic sedimentary rock.
Grey
Sandstone
Greywacke or Graywacke (German grauwacke, signifying
a grey, earthy rock) is a variety of sandstone generally
characterized by its hardness, dark colour, and poorly
sorted angular grains of quartz, feldspar, and small rock
fragments or lithic fragments set in a compact, clay-fine
matrix. It is a texturally immature sedimentary rock
generally found in Palaeozoic strata.
Halite
Halite is sodium chloride, NaCl, the same mineral you use
as table salt. It is the most common halide mineral. A
chemical sedimentary rock that forms from the
evaporation of ocean or saline lake waters. It is rarely
found at Earth's surface, except in areas of very arid
climate.
Shale
Gypsum
Jasper
Siltstone
Arkose
Shale is a fine-grained sedimentary rock that forms from
the compaction of silt and clay-size mineral particles that
we commonly call "mud". This composition places shale in
a category of sedimentary rocks known as "mudstones".
Shale is distinguished from other mudstones because it is
fissile and laminated. "Laminated" means that the rock is
made up of many thin layers. "Fissile" means that the rock
readily splits into thin pieces along the laminations.
Gypsum is an evaporite mineral most commonly found in
layered sedimentary deposits in association with halite,
anhydrite, sulfur, calcite and dolomite. Gypsum
(CaSO4.2H2O) is very similar to Anhydrite (CaSO4). The
chemical difference is that gypsum contains two waters
and anhydrite is without water. Gypsum is the most
common sulfate mineral.
Jasper is a common impure variety of quartz. It is usually
red, yellow or brown. Jasper has been known to come in
more uncommon colors such as green. It can be intensely
polished and is used for vases and seals. Banded Jasper
occurs when the colors are in stripes and/or bands.
Jaspilite is a banded iron formation rock that usually
contains distinctive bands/stripes of jasper. Jasper is
commonly used for ornamentation or as a gemstone.
Patterns are due to mineral impurities and sediments
including with volcanic ash. Formations are mainly due to
mineral impurities as well as erosion.
Siltstone is a clastic sedimentary rock that forms from siltsize (between 1/256 and 1/16 millimeter diameter)
weathering debris. The silt in this siltstone is unusually
pure, containing very little sand or clay. The absence of
clay matrix makes siltstone soft and crumbly, even though
this specimen is many millions of years old. Siltstone is
defined as having twice as much silt as clay.
Arkose is a raw, coarse-grained sandstone, deposited
very near its source, that consists of quartz and a
significant proportion of feldspar. Arkose is known to be
young because of its content of feldspar, a mineral that
usually degrades quickly into clay. Its mineral grains are
generally angular rather than smooth and rounded,
another sign that they were transported only a short
distance from their origin. Arkose usually has a reddish
color from feldspar, clay and iron oxides—ingredients that
are uncommon in ordinary sandstone.
Mudstone is made up of tiny clay particles (less than
0.05mm) that can’t be seen with the naked eye. These
tiny particles are deposited in quiet low-energy
environments like tidal flats, lakes, and the deep sea.
Mudstone
Dolomite
Fossils in
Sandstone
Dolomite is a carbonate mineral. It is composed mainly of
Calcium and Magnesium Carbonate found in the crystals.
Dolomite rock is also known as dolostone. Dolostone is
made up of Dolomite mineral as well as Calcium
Magnesium Carbonate and other materials. Dolomite that
is partially replaced by Limestone is referred to as
magnesian limestone by most geologists.
Trace fossils are geological records of biological activity.
Trace fossils may be impressions made on the substrate
by an organism: for example, burrows, borings
(bioerosion), urolites (erosion caused by evacuation of
liquid wastes), footprints and feeding marks, and root
cavities. The term in its broadest sense also includes the
remains of other organic material produced by an
organism