GeologyRocks

Calcite

Calcite is a mineral composed of Calcium Carbonate (CaCO₃). It exists as two forms, low and high Magnesium (Mg). Only low Mg is stable at the Earth's surface. Calcium Carbonate can also be found as aragonite, which is a polymorph of calcite. Calcite crystals may also show double refraction.

Cambrian

The earliest defined geological period spanning 542-483Ma. Time before the Cambrian is referred to as the Pre-Cambrian, making the Cambrian the first period of the Palaeozoic Era. All fossils from this period are marine and the beginning of this period saw the Cambrian Explosion; an apparent burst of evolution.

The Cambrian is split into four Epochs, Lower Series, Series 2, Series 3 and Furongian.

Carboniferous

The fifth period of the Palaeozoic. Spans 359-299Ma, and is famous for the extensive coal beds found throughout the UK.

Cast

The infill of a fossil mould.

Chalk

A fine grained, white calcium carbonate composed of coccoliths. Common in the Cretaceous of western Europe.

The White Cliffs of Dover are a classic example of chalk cliffs.

Chert

Microcrystalline silica (SiO₂). Flint is the best known example.

Citrine

Variety of quartz. Yellow-orange in colour.

Cladogenesis

The evolution of two or more daughter species from a single parent species by the splitting of a lineage.

Cleavage

The distinct planes of weakness that a mineral breaks along. The picture below shows clear cleavage lines.

Cline

A gradual change in an allele frequency or in the mean of a character over a geographic boundary.