Saturday, October 15, 2016

Howlite, an evaporite mineral from southern California

This post concerns an interesting mineral which can be found not too far from where I live in southern California. The mineral is howlite (also called “white turquoise” by some collectors). It is a borate mineral (calcium borosilicate hydroxide) that is found in evaporite deposits. In my area, these kind of deposits occur in the middle Miocene Mint Canyon Formation in Tick Canyon, Soledad basin. The howlite found there occurs in its most common form, as nodules. This locality is known for its high-quality howlite, including some rarely found crystals of this mineral. To see pictures of these crystals (I do not have any), go to Wikipedia and type in the word “howlite.”

Nodule of howlite, 5 cm width.
The nodules are white with fine gray or black veins, which create an erratic weblike patterns. The nodules are used in jewelry. They are easily dyed to imitate other minerals, especially turquoise, which also commonly has a veining pattern.

This picture shows some of the variation found in nodules of howlite. Nodule is 5 cm width.

In Tick Canyon, howlite was mined for a time, along with other evaporate minerals. The mining operation has long since closed down.

No comments:

Post a Comment