Black Hills Mineral Collection

The major mineral collection displayed in the Museum of Geology consists of an overview of some of the best examples of species of minerals from all over the world arranged according to their chemical compositions. One of our featured exhibits is the W. L. Roberts Hall of Black Hills Minerals. In the Roberts Hall are exhibited fine examples of minerals from the Black Hills of South Dakota and Wyoming which were described in Mineralogy of the Black Hills (Roberts and Rapp, 1965).

Featured cabinets exhibit groups of minerals including:

Fairburn Agates are collected east of the Black Hills near the town of Fairburn, S.D. These prized agates are finely banded with various thin layer of quartz forming beautiful fortification patterns in these semiprecious stones.

Rose Quartz is a pink variety of quartz found in many Black Hills Pegamatites. It is sometimes carved or polished into cabrochons and occassionally faceted.

Minerals of the Homestake Gold Mine include fine examples of over xxx minerals which occur in the Homestake Gold Mine at Lead, S.D. including several specimens of native gold.

Cave Deposits are found in the many caves of the Black Hills, mostly developed in the Pahasapa Limestone of Mississippian age. Included are fine examples of stalctites, frostwork, boxwork, popcorn, and dogtooth spar. Nearby are mounted maps of Wind Cave and Jewel Cave.

Pegmatite Minerals are exhibited from the numerous pegamatites of the Black Hills. Pegmatite is coarse grained granite, with grains or crystals up to eight feet in diameter and over 100 feet long! This large crystal size indicates these granitic rocks cooled very slowly at great depths within the Earth's crust. Uplift and erosion of the Black Hills has raised them and exposed them at the surface where they have been mined in the past (and finer grained portions of the Harney Batholith also carved to form Mt. Rushmore and now Crazy Horse Monuments). The large grain size of the pegmatite dikes allowed the complex mineralogy to be exploited by early miners to remove economic minerals such as beryl, spodumene, muscovite, orthoclase, columbite/tantalite, rose quartz, and many others. Primary phosphates have been modified forming rare and unusual secondary phosphates.

Sedimentary Minerals include numerous minerals collected from the sedimentary rocks around the Black Hills, including golden barite crystals.