Minerals

A starburst or red tourmaline stands out against its white surroundings. Tourmaline is the name for a group of related minerals; red tourmaline also can be called rubellite. Semiprecious gemstones, tourmalines belong to a family of borosilicate minerals. They come in a range of colors from red to black and are found from Madagascar to Maine.
Photograph by Scott Camazine/Alamy

The needle-like crystals of this mesolite deposit from India give it a dandelion's form. Its crystalline structure formed inside a bubble of volcanic gas as igneous rock cooled. Mesolite's many striking crystal formations make it a popular mineral for collectors.
Photograph by Natural History Museum/Alamy

Mammoth Cave in Kentucky contains gypsum formations that mimic flowers. The mineral gypsum contains calcium sulfate (calcium, sulfur, oxygen) and water. The gypsum precipitates out of water in the cave, creating these subterranean forms over time.

Mineral deposits in Lechuguilla Cave take on fantastical forms in Carlsbad Caverns National Park, New Mexico. Stalactites of calcite and a small aragonite formation appear as if in a magical backdrop. Calcite and aragonite are the two crystal forms of calcium carbonate, a property of minerals geologists call dimorphism. Their crystal structure sets them apart: calcite forms hexagons and aragonite forms rhombohedrons.

Azurite crystals from Arizona seem to pulse with color. The mineral azurite—a copper ore—consists of blue basic carbonate. Azurite's brilliant color adds to its popularity in creating semiprecious stones.
Photograph by Steve Hamblin/Alamy

Mineral deposits add color to the landscape. Minerals have existed since the very beginnings of the Earth, forming as our planet cooled. Many form deep beneath the Earth's surface, but some are found on the surface.
Photograph by Thinkstock/Corbis

A volcano in Java, Indonesia, produces yellow deposits of sulfur that prove to be easy but dangerous pickings for a man collecting the mineral. Sulfur often combines into sulfides or sulfates. The nonmetallic element heals and destroys: Doctors use sulfur to treat fungal infections, but it is also a component of gunpowder. Sulfuric acid is an important industrial agent.
Photograph by Kirk Treakle/Alamy

A pink chalcedony shows off its beauty. Chalcedonies include many types of cryptocrystalline quartz gems and feature a number of different colors. Geologists can tell a chalcedony from the arrangement and structure of its crystals.
Photograph by blickwinkel/Alamy



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