The Division of Mineralogy oversees a historically important worldwide collection of over 40,000 specimens, most of them catalogued into a systematic collection created from the original Yale Peabody Museum holdings and the G. J. Brush Mineral Collection. The collection includes 36 documented type specimens, as well as other presumed type specimens that require further documentation.

The largest and most important collection in the Division is the G. J. Brush Mineral Collection. Other collections include the Blum Collection of pseudomorphs and the Lazard Cahn Collection of micromounts.

In addition to the many referenced specimens, the collection contains suites of material from localities that no longer exist, early prospecting material, a collection of gemstones, and a sizeable collection of Connecticut minerals.