The rock, or petrology, collection consists of several thousand hand samples and a number of drill cores from around the world. This collection is primarily used for research and parts of it are available for loan to researchers outside the museum.

The petrology collection includes samples of:

Layered Mafic Intrusions

"Snowball" of orthopyroxene (brown) and plagioclase (white) in banded norite in the Stillwater Complex, Montana

Layered mafic intrusions are large igneous bodies that are layered similarly to sedimentary rocks. Many widely used and precious metals such as chromium, platinum, palladium, and nickel can be found in layered intrusions, and thus they can be extremely important natural resources. The Bushveld Complex in South Africa provides most of the world's chromium. The largest Pt-Pd mine in the U.S. is in the Stillwater Complex in Montana. Samples from the Bushveld are currently on display in the Mineral Hall.

Rock types include:

• anorthosite (plagioclase)
• bronzitite (bronzite, a type of orthopyroxene)
• chromitite (chromite)
• dunite (olivine)
• gabbro (olivine, pyroxene, plagioclase)
• harzburgite (olivine, bronzite)
• norite (orthopyroxene, plagioclase)
• pegmatoid (usually a pyroxenite or gabbro with particularly large crystals)
• pyroxenite (orthopyroxene, clinopyroxene)
• troctolite (olivine, plagioclase)
• websterite (orthopyroxene, clinopyroxene)
• Pt-Pd ore
• massive Ni-Fe sulfides

These layered mafic intrusion samples are from:

• Stillwater, MT
• Great Dike, Zimbabwe
• Bushveld Complex, South Africa - Rustenberg section
• Bushveld Complex, South Africa - Atok section
• Noril'sk Intrusion, Siberia
• Koitelainen, Finland

Kimberlites

Kimberlites are ultramafic igneous bodies that contain a variety of minerals and inclusions of other rocks. Kimberlites are particularly important economically speaking because they are the major source of natural diamonds. Kimberlites at the museum are also used to study the silicon carbide mineral moissanite.

Mantle Xenoliths

Mantle xenoliths are ultramafic rocks that are found in the crust of the earth, but which were apparently formed within the earth's mantle. "Xenolith" actually means "foreign rock". Mantle xenoliths are found within some basalts and in kimberlites. Our collection includes:

• peridotites
• dunites (olivine)
• harzburgites (olivine, orthopyroxene)
• lherzolites (pyroxene, olivine)
• wehrlites (olivine, clinopyroxene)
• pyroxenites
• clinopyroxenites
• orthopyroxenites
• websterites (orthopyroxene and clinopyroxene)

Lower Crustal Rocks

Xenoliths from the metamorphosed lower crust are also found in kimberlites and basalts.

• amphibolite, hornblendite
• granulite
• eclogite

Volcanics

The museum's collection includes many different kinds of volcanic rocks, rocks that solidified on the surface of the earth. These include basalts, porphyry (volcanic rocks with large crystals in a fine-grained matrix), obsidian, and ash from recent eruptions. Many of the basalt samples contain mantle xenoliths.

Stalagmite of basalt from Hawaii

• Hawaii
• Zabargad, Egypt
• Mt. Pele, Martinique
• Vesuvius, Italy
• Mt. St. Helens, WA
• Arizona
• New Mexico
• Mt Lassen, CA
• Soufriere, St. Vincent
• Newer Volcanic Field, Australia
• Pinacate, Mexico
• Massif Central, France

Carbonatites

Carbonatites are igneous rocks, both plutonic and volcanic, primarily composed of calcium, magnesium, and sodium carbonates.

Various suites from around the world

• Simplon Tunnel, Switzerland
• New Hampshire, Hitchcock Collection
• Vermont, Hitchcock Collection
• New York State
• New York City
• Mexico
• Italy
• 40th Parallel
• Greenland, Crocker Land Expedition
• Building Stones