Rhodonite variety Fowlerite, Sterling Hill, Franklin, New Jersey
Mimetite, San Pedro, Corellitas, Mexico
Azurite, Copper Queen Mine, Bisbee, Arizona
Rhodochrosite, Hotazel Mine, Kalahari field, Northern Cape Province, South Africa

Quartz Variety Amethyst with Calcite in Basalt

Minas Gerais, Brazil

Geodes such as this one usually contain interesting crystals and can range from pea-sized specimens to those as large as a room! A geode is simply a hollow, irregularly rounded rock with inward-pointing crystals. Our Treasures of the Mineral World gallery has a large geode that you can touch.

Sphaerocobaltite

Shaba Region, Democratic Republic of the Congo (Zaire)

Scheelite

Tae Wha Mine, Chungiu, Chungchongpukdo, South Korea

Wolframite

Panasqueira, Portugal

The largest percentage of minerals form out of cooled magma (lava) erupted from volcanoes or other catastrophic phenomena. What minerals form depends on the composition of the magma. The way the minerals form depends on how quickly they cool, what other minerals or chemical substances are present, and what pressures the formation is subjected to.

Quartz with Siderite

Morro Velho Mine, Nova Lima, Minas Gerais, Brazil

Beryl Variety Morganite

Governador Valadares Gilileia, Minas Gerais, Brazil

Pyromorphite

Society Girl Mine, Moyie, British Columbia

Many crystal formations are either associated directly with precious minerals or are cut and polished into precious and semi-precious gemstones. The quartz-siderite specimen seen here was taken from a gold mine that operated between 1834 and the 1960s. The morganite in this photo is a cousin to aquamarine and emerald, and has only recently been accepted as a gemstone.

Calcite

Lyons County, Nevada

Calcite and quartz can grow into massive structures, but calcite can also form delicate almost tree-like (or "dendritic") crystalline shapes like the example shown here. Naturally occurring structures such as these are rare. Far more often minerals occur in tiny individual crystals spotted throughout a rock matrix, resulting in a grainy appearance.