Benitoite: The mineral benitoite information & picture

About

Benitoite was first discovered in 1907, and upon its initial discovery was thought to be Sapphire. The crystal structure of Benitoite is unique, and is the only significant mineral in its crystal class. It crystallizes in a rare hexagonal sub-class called ditrigonal-dipyramidal.

Most Benitoite crystals were originally deeply embedded in thick Natrolite; specimens are prepared for collectors by dissolving the surrounding Natrolite in acid to expose the Benitoite crystals. The blue Benitoite on a white Natrolite matrix and usual association with black Neptunite makes a very aesthetic mineral specimen.

Benitoite is named after its locality in San Benito Co. in California, where this mineral was first found in a remote area far from civilization. This region is the only source of Benitoite, aside from some very sporadic and extremely limited occurrences worldwide.

For additional information, see the gemstone section on Benitoite.

Crystal Forms & Aggregates

In well-formed, tabular crystals that are triangular in shape, often with slightly flattened points or sub-triangular points. Crystals may be in isolated crystals or interconnected. Twinning as stubby hexagonal prisms are also known, and a rare oddity is a perfectly aligned penetration twin shaped as a star of David.

Other ID Marks

Strongly fluorescent light blue in shortwave ultraviolet light. Some crystals fluoresce a dull red in longwave.

Striking Features

Color, crystal habits, locality, and mineral associations

Environment

In a hydrothermal replacement deposit composed of Natrolite veins in Glaucophane schist in Serpentine.

Uses

Benitoite is cherished by collectors as a rare and valuable mineral. It is also cut as as an exquisite rare gemstone.

Noteworthy Localities

The only significant locality for Benitoite is the Diablo Range, near the headwaters of the San Benito River, in the Southern tip of San Benito Co., California. Virtually all collectors specimens for this mineral are from this area. The now-closed Dallas Gem Mine in the Diablo Range has been the source of most of the available material and the largest crystals. Other localities in the area include the Santa Rita Peak, the Victor Claim, the Number One Mine, and the Junnila Mine. In Japan, a very limited occurrence of small gemmy Benitoite is Hashidate, Itoigawa, Niigata Prefecture, Japan.