NEPTUNITE

Benitoite’s Uncommon Partner

- BOB JONES

Named for the Roman Sea God, Neptunus, neptunite is often found with California State’s official gem mineral benitoite. Neptunite is found with such a bright blue gemmy associate that it is so popular and rare that everyone wants to own benitoite. No wonder neptunite has not been given the attention it deserves. It is understandable that benitoite tends to eclipse neptunite for attention. But neptunite is a beautiful mineral in its own right. It appears as a lustrous, black, opaque crystal on a stark white matrix. Crystals can measure up to two inches with perfectly terminated prismatic faces in nice-sized display specimens.

Neptunite is found in the San Benito Mountains, locked in a contrasting snow-white natrolite matrix. The specimens are very attractive and well worth collecting as the lustrous stark black crystals contrast nicely with blue benitoite and white natrolite matrix.

Neptunite is very complex chemically composed of sodium, potassium, lithium, iron, manganese, titanium silicate. It is also found elsewhere as a high manganese neptunite and so-called mangan-neptunite. This forms when manganese substitutes for some of the iron atoms in neptunite’s chemistry.

The neptunite from California is the iron end member of a series, with mangan-neptunite the opposite member. Localities that yield mangan-neptunite are nepheline syenite pegmatite deposits, unlike the San Benito source.