Browse an overview of this volcanic rock's origin, formation, components, and physical characteristics.

Study this volcanic silica glass and view sample images. Learn about its uses, physical properties and chemical composition.

Learn about this mineral made of magnesium and iron silicate, including its physical appearance and geographical origin.

Introduces the three principal substances in this group - forsterite, olivine, and fayalite. Provides details on their industrial applications.

Learn about the chemical make-up and appearance of this black or white mineral also used as a gem.

Discusses this substance's common and precious forms, and explains why it is not actually a mineral, but rather a mineraloid.

Learn about the various components of this mineral formed of hydrated silica. Certain transparent varieties are recognized as gemstones.

Concise virtual encyclopedia describes the origin, production, and appearance of these gems formed from the secretion of certain mollusks.

Provides a scientific definition of this igneous rock found on the surface of older mountain ranges through out the world.

Learn about the different types and components of peridotite, the igneous rock that makes up the Earth's mantle.

Provides a definition of the black ore which is a significant source of uranium. Includes details on where it is found.

Read a definition of this variety of igneous rock known for its large crystals.

Brief description of this igneous rock includes details on its origins and structure.

Describes the crystalline forms taken by this variety of iron sulfide. Outlines its properties, and provides photos of samples.

Encyclopedia entry provides details on iron sulfide, known colloquially as fool's gold.

Explains the composition of these silicate compounds, and provides examples of representative minerals.

Explore the composition and characteristics of this Sulfide. Order samples online.

Find out more about this common and often beautiful variety of silicon dioxide. Explore an extensive photo gallery.

Discover details on this crystal's chemical make-up, learn how it is formed, and find background on its commercial uses.

Learn about a crystalline substance used to make ancient arrowheads.

Encyclopedia entry offers facts on this rock's composition and the formations in which it is found.

Learn about a volcanic rock which shares the chemical composition of granite.

Defines this broad category of mineral compounds formed by natural processes. Provides details on the different varieties.

Photos of this prized gem are accompanied by details on its composition and crystalline structure.

Details the composition, origins, characteristics, and uses of this titanium oxide ore.