Most rocks are made of various types of minerals, but some are made of animal shells or compressed plant parts. Minerals are natural inorganic solids with a specific chemical composition. Crystals are expressions of the ... More »

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Raphide crystals are acicular crystals that occur in bundles in the cells of many types of plants. They are usually made of calcium oxalate. More »

The defining feature that separates lead crystal from crystal glass is the object's lead content. Lead crystal contains between 24 percent and 35 percent lead, while crystal glass is made by replacing lead with zinc oxid... More »

Sedimentary rocks are made of minerals and debris that have been weathered or eroded from rocks over long stretches of time. This sediment can be laid down by water, by the movement of earth or glaciers, by evaporation o... More »

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Igneous rocks that are allowed to cool more slowly form larger crystals, while igneous rocks that cool quickly form smaller crystals. It is simply a matter of time. The longer it takes for magma to cool, the more time is... More »

Magnetite forms in small quantities interspersed with many iron-rich minerals, but only forms bodies of crystals on its own when mafic magma, a very liquid magma laden with heavy elements, cools sufficiently slowly for i... More »

A silica tetrahedron is the basic unit of silicates, which are minerals in the Earth's rocks. The tetrahedron comprises a single positively charged silicon molecule surrounded by four negatively charged oxygen molecules.... More »