Geology or Related Geological Terms +

A substance used for cutting and polishing or for removing small amounts of the surface of hard materials.

There are two types: natural and artificial abrasives, and their hardness is measured using the Mohs scale (available in this list), a scale used to measure the hardness of minerals, with talc at zero and diamond at ten. Each mineral on the scale is hard enough to scratch the one below it in the scale.

Time before the present stated in years; referring to geologic events, generally based on measurement of radioactive decay rates and products of minerals or rock substances; such as, the uraniumlead method, carbon-14 method, etc.

1. Deep within the earth, generally signifying a depth of some miles; also, plutonic.
2. Deep in oceans or lakes, well beyond depth of light penetration, commonly referring to depths of 1,000 feet or more in lakes nd 6,000 feet or more in oceans.

Describing igneous rocks having silica (SiO₂) content greater than two-thirds of total constituents; such as, rhyolite, granite, etc.

The magnetic equator which is an imaginary line near the Equator, where a compass needle balances horizontally, the attraction of the north and the south magnetic poles being equal.

Adjustment of structures or modes of living (including methods of reproduction) that better fit an organism to its environment, thereby favoring successful competition with other organisms and survival.

Differentiation of related organisms by adaptation to dissimilar environments or modes of living (as horses, wolves, seals, and whales, and all mammals).

A term applied to coast line, drainage pattern, or individual stream with placement controlled by rock hardness or structure or both; such as, so-called subsequent streams of Appalachian Mountains flowing in weak rocks parallel to strike.

A reference to air or atmosphere; subaerial conditions or processes on land, because of being directly under the atmosphere.

1. Banded or cloudy quartz with a waxy appearance.
2. Cryptocrystalline with crystals that are too small to be seen with an optical microscope.

It contains silica that is composed of cloudy and banded chalcedony (translucent or grayish semiprecious stone), sometimes mixed with opal, which forms in rock cavities.

Applied to silicified fossil including wood, invertebrate shells, and vertebrate bones with the appearance of agate.

Any time span in earth history; such as, absolute age of rock or mineral, relative age of one rock unit compared with another, "age of reptiles", referring to the time when reptiles were dominant animals on the earth.

Time represented by the time-stratigraphic unit called Stage (initial capital letter used in formal nomenclature).

Accumulation of coarse, angular or subangular pyroclastics.

Upward building of a surface by deposition of sediment.