Library: Geology by Credo Reference: Rocks and Minerals

Classification of Rocks

Sedimentary Rocks: Topic Page
Sediments are loose, unconsolidated rock particles and ions (i.e., charged atoms) dissolved in aqueous solutions. Sedimentary rocks, which constitute about 75% of all rocks exposed at the surface of the Earth, form when the particles are cemented together or when crystals precipitate from the solutions.
Igneous Rocks: Topic Page
The so-called crust of the Earth is about 35 km thick under the continents but averages only some 7 km beneath the oceans. It is formed mainly of rocks of relatively low density.
Metamorphic Rocks: Topic Page
Rock altered in structure, composition, and texture by pressure or heat after its original formation.

Types of Rocks

Andesite: Topic Page
The volcanic equivalent of diorite, andesite is fine grained or porphyritic, and primarily consists of the plagioclase feldspar minerals andesine and oligoclase, plus one or more of the dark, ferromagnesian minerals, such as pyroxene or biotite.
Anorthosite: Topic Page
An intrusive igneous rock, anorthosite is composed of at least 90 per cent calcium-rich plagioclase feldspar – principally labradorite and bytownite.
Basalt: Topic Page
Fine-grained rock of volcanic origin, dark gray, dark green, brown, reddish, or black in color.
Chalk: Topic Page
A soft, fine-grained, easily pulverized, white to grayish variety of limestone, chalk is composed of the calcite shells of minute marine organisms.
Diabase: Topic Page
Colour When fresh it is black, dark grey or green; may be mottled black and white.
Diorite: Topic Page
Colour Speckled black and white in hand specimen; occasionally shades of dark green or pink. The dark minerals are more noticeable than in gabbro.
Dolostone: Topic Page
Colour: White, cream or grey, but often weathers brown or pinkish. Texture: Coarse, medium or fine; compact, sometimes earthy.
Gabbro: Topic Page
Colour Grey, dark grey, black; may have a bluish or greenish tone. Colour index 30 to 90; with a decrease of coloured minerals gabbro grades into anorthosite, and with an increase it grades into pyroxenite and peridotite.
Granite: Topic Page
Coarse-grained intrusive igneous rock, typically consisting of the minerals quartz, feldspar, and biotite mica. It may be pink or grey, depending on the composition of the feldspar. Granites are chiefly used as building materials.
Kimberlite: Topic Page
The major source of diamonds, kimberlite is a form of peridotite. It is mica-rich, often with well-formed crystals of brown phlogopite mica.
Lava: Topic Page
Molten rock that erupts on the earth's surface, either on land or under the ocean, by a volcano or through a fissure.
Marble: Topic Page
Metamorphic rock composed wholly or in large part of calcite or dolomite crystals, the crystalline texture being the result of metamorphism of limestone by heat and pressure.
Pegmatite: Topic Page
Pegmatite is the name given to very coarse-grained, igneous rocks.
Periodtite: Topic Page
One of the most economically important rocks, peridotite is the ultimate source of all chromium ore, and its variety kimberlite is the source of all naturally occurring diamonds.
Pumice: Topic Page
A very porous, froth-like volcanic glass, pumice is created when gas-saturated liquid magma erupts like a fizzy drink released from a shaken bottle, and cools so rapidly that the resulting foam solidifies into a glass full of gas bubbles.
Rhyolite: Topic Page
Color Usually light coloured; white, grey, greenish, reddish or brownish. The colour may be even, or in bands of differing shades.
Syenite: Topic Page
Syenites may be visually similar to granite, and are often confused with it, but they can be distinguished from it by the absence or scarcity of quartz.
Tektites: Topic Page
A naturally occurring, silica-rich (65%–80% SiO2) glass resembling obsidian and sometimes shale, and is normally jet black to olive green.
Tuff (Volcanic Ash): Topic Page
TUFF IS A BROAD TERM used to include any relatively soft, porous rock made of lithified pyroclastic minerals (ash and other sediments ejected from volcanic vents).

Earth Materials

Water: Topic Page
Chemical compound of hydrogen and oxygen elements - H2O. It can exist as a solid (ice), liquid (water), or gas (water vapour).
Sand: Topic Page
Rock material occurring in the form of loose, rounded or angular grains, varying in size from .06 mm to 2 mm in diameter, the particles being smaller than those of gravel and larger than those of silt or clay.
Mineral: Topic Page
Inorganic substance occurring in nature, having a characteristic and homogeneous chemical composition, definite physical properties, and, usually, a definite crystalline form.
Rock: Topic Page
Constituent of the Earth's crust composed of minerals or materials of organic origin that have consolidated into hard masses.

Minerals

Antimony: Topic Page
Antimony exists in two allotropic forms (see allotropy); the more common is silvery blue-white and has a rhombohedral crystalline structure.
Barium: Topic Page
Barium is a soft, silver-white, chemically active, poisonous metal with a face-centered cubic crystalline structure.
Beryllium: Topic Page
Beryllium is a strong, extremely light, high-melting, silver-gray metal with a close-packed hexagonal crystalline structure
Cobalt: Topic Page
Cobalt is one of the mineral elements known to be essential for health, but only required in minute amounts - a trace element.
Copper: Topic Page
Red-brown, very malleable and ductile, metallic element, atomic number 29, relative atomic mass 63.546.
Gold: Topic Page
Gold is very ductile and is the most malleable metal; it can be beaten into extremely thin sheets of gold leaf.
Lead: Topic Page
Lead (Pb) has been used since ancient times. It is commonly used in modern petroleum engineering, atomic reactors, and many organic (synthetic) compounds.
Lithium: Topic Page
Lithium is a soft, silver-white metal.
Manganese: Topic Page
Manganese is a pinkish-gray, chemically active metal.
Mica: Topic Page
General term for a large group of minerals, hydrous silicates of aluminum and potassium, often containing magnesium, ferrous iron, ferric iron, sodium, and lithium and more rarely containing barium, chromium, and fluorine.
Molybdenum: Topic Page
Molybdenum is a hard, malleable, ductile, high-melting, silver-white metal with a body-centered cubic crystalline structure.
Nickel: Topic Page
Nickel is a hard, malleable, ductile, lustrous, silver-white metal with a face-centered cubic crystalline structure.
Platinum: Topic Page
Pure platinum is a malleable, ductile, lustrous, silver-white metal with a face-centered cubic crystalline structure.
Quartz: Topic Page
The most abundant mineral, quartz is found in myriad colours, shapes, and varieties.
Silver: Topic Page
Pure silver is nearly white, lustrous, soft, very ductile, malleable, and an excellent conductor of heat and electricity.
Sulfur: Topic Page
Brittle, pale-yellow, non-metallic element, atomic number 16, relative atomic mass 32.064.
Tantalum: Topic Page
Tantalum is a rare, hard, blue-gray metal with a body-centered cubic crystalline structure. I
Tungsten: Topic Page
Tungsten is a very hard, silver-white to steel-gray metal with a body-centered cubic crystalline structure.
Uranium: Topic Page
Hard, lustrous, silver-white, malleable and ductile, radioactive, metallic element of the actinide series, atomic number 92, relative atomic mass 238.029.
Vanadium: Topic Page
Vanadium is a soft, ductile, silver-grey metal.
Zinc: Topic Page
Zinc is a lustrous bluish-white metal.