Geology or Related Geological Terms +

Without form, referring to rock or other substance lacking observable texture.

Four-legged vertebrate (tetrapod) that reproduces only in an aquatic or very moist environment, breathes by means of gills during at least early life, and develops lungs for air breathing; known from Devonian to Recent.

Ferromagnesian silicate mineral, common constituent of igneous and metamorphic rocks.

Class of marine mollusks, generally called chitons, characterized by a large flat foot used in crawling and a dorsal side protected by jointed transverse plates.

Extrusive igneous rock containing many gas-formed vesicles more or less filled by secondary minerals; such as, quartz, calcite, zeolites, etc.

Individual mineral-bearing vesicle of an amygdaloid.

Pertaining to organisms; such as, many bacteria, that are able to live in an environment that lacks free oxygen.

Branching repeatedly with reunion of the branches to form a netlike pattern.

Aluminum silicate, a white to pinkish mineral crystallizing as square-based or rhombus-based prisms.

It is common in metamorphic rocks formed from clay sediments under low pressure condition. Andalusite, kyanite, and silimanite are all polymorphs (a compound that has several crystalline forms) of aluminum silicate.

Extrusive igneous rock distinguished by content of silica lower than in rhyolites and especially by the nature of its plagioclase feldspar.

1. A surface that separates younger strata from eroded, dipping, older strata and represents a gap in the geologic record.
2. Structural discordance of stratified rocks produced by erosion of the older beds and deposition of younger beds on the edges of the eroded rocks.

Angular unconformities signify deformation of the older strata prior to deposition of the younger ones.

They may be simulated by cross-bedding and by faulting, distinction of which from angular unconformities generally is recognized easily by various criteria.

Rock composed mainly of anhydrite.

Also called anhydrock, a much less suitable name, because "stone" rather than "rock" is used by custom in nomenclature of many lithified sedimentary deposits, as sandstone, limestone, etc.

1. A mineral of a white or a slightly bluish color, usually massive.

It is anhydrous sulphate of lime, and differs from gypsum because it does not contain water (whence the name).

2. A mineral consisting of anhydrous calcium sulfate, commonly formed as massive or laminated evaporites; which may be altered by hydration to gypsum, as in weathering.

A compact, granular sedimentary rock harder than gypsum, composed essentially of calcium sulfate, resembling marble and deposited by evaporation.

1. A type of worm characterized by numerous appendage-bearing or leg-bearing body segments.
2. An invertebrate organism with a flat body that is divided into segments.

Earthworms and leeches are annelids of the Phylum Anelida.