The Mineral Collection consists of approximately 100,000 specimens and is significant by virtue of its size, broad representation of species and occurrences, the quality of the exhibit specimens, and the large number of type, described, and illustrated specimens.
With the exception of the micromounts, the collection is catalogued as a single entity but is physically organized into several sub collections. Notable holdings include the minerals from the zinc mines at Franklin, New Jersey (4,000 specimens), from the Tsumeb Mine in Namibia (900 specimens), and from the local New England region (7,000 specimens).
The paragenetic series are suites from particular occurrences assembled to study how minerals form. These are fundamentally geological in nature as opposed to the chemical character of the systematic series. For thirty years or more Professor Palache assigned paragenetic suites that he'd field collected in New England to his mineralogy class for term papers, several of which were later published. Building on this foundation most of the specimens from the New England region have been physically moved into the paragenetic suites both to place them in their geological context and to gain precious space in the cabinets holding the systematic series.
Minerals in the systematic series are organized chemically. About 4,000 of the finest specimens are displayed in the HMNH mineral gallery. The rest - the "working" collection - is housed behind the scenes. It archives specimens used in past studies and holds material suitable for future investigation. This is the primary and largest part of the mineral collection.
Micromount Collections consist of small mineral specimens mounted in one-inch boxes for viewing through a microscope. The historical micromount collection (3,200 mounts) is part of Albert F. Holden's personal collection left to the university in 1912. During the 1990s a contemporary micromount collection of 6,600 mounts was built by Stephen and Janet Cares. It incorporates the collections of Gilbert George and Leland Wyman as well as many specimens supplied by the Cares. The micromount collections are rich in rare species and significantly supplement the collection of hand specimens.
The Gemstone Collection consists of approximately 1,200 gems and is broadly representative, though its strength lies in New England gems which account for roughly 60% of the collection. Its systematic development begin in 1923 when Albert F. Holden left the museum a generous endowment to help fund new acquisitions. From that point on the collection grew considerably under the direction of curator Charles Palache. In the late seventies an unprecedented influx of gemstones into the collection influenced the museum's decision to separate the gems from the mineral collection into their own distinct collection. Though the gem collection contains cabochons, carvings, and other lapidary art material, the majority of items are faceted stones. Arguably the most prized and well known piece of the collection is the Hamlin Necklace which was created by Augustus Hamlin to showcase eighteen tourmalines from the Mount Mica Mine he owned and operated. The necklace was bequeathed to the museum in 1934.