Saturday, April 07, 2012

G is for Garnet


G is for Garnet:

Garnets, what color are they anyway?

Most of the time when someone mentions garnets you think of deep red-wine color. But this is just one of the many colors a garnet can be.

Garnet Crystal From China

There are 7 different varieties of garnet and a range of colors that is most impressive.
Each variety of garnet has the same physical properties such as hardness, crystal shape (cubic), etc. The real difference is in the chemical makeup. All the different varieties of garnet are Aluminum Silicates. Mg, Fe, Mn, Ca, Cr, and water can all be attached to the front of the formula to change the type of garnet ( and the color ) it forms. For example...

Pyrope is red-wine colored by Mg.
Almandine is brown caused by Fe.
Spessartine is brown to lime green caused by Mn.
Grossular is red-brown to raspberry pink caused by Ca..
Andradite is brown to brown-red caused by Ca-Fe mixed.
Uvarovite is a bright green caused by Ca-Cr mix.
Hydrogrossular is unimpressive brown caused by Ca and water.


There are other types of garnets that are sub-species of the species listed above
.
Demantoid ( brilliant green with the luster of a diamond ), Melanite (black), and Topazolite (yellow to yellow-brown) are all forms of andradite.

Rhodolite is a very rose-red form of pyrope.

Hessonite (cinnamon colored), Tsavorite (emerald-green colored), and Leuco (clear) are all forms of grossular.

One other interesting  characteristic of  garnets is that sometimes the different types will mix together. So the outside of the crystal is almandine and the inside is spessartine. This is called “solid solution”. It has to do with the chemistry of the environment when they are forming.

“What are garnets good for?” you ask. Well they don’t have any special purpose. Most are used for abrasives as they are very hard and tough. They are also used for gemstones. Many of the clean stones are cut into gemstones that now sell for hundreds of dollars per carat. My favorite use is as crystals in my collection.

Where can you go find a garnet?  Garnets are not rare on this planet. In fact, they are abundant. There are many places in Utah to collect garnets.

The Alta stock up big cottonwood canyon has a nice deposit of almandine that are not gem quality but show really nice structure.

Gold Hill mine and the surrounding area have lots of garnets.

The Thomas Range (Topaz Mountain area) has garnets pseudomorphed to hematite and often have bixbyites attached to them.

There is a really nice deposit of pale green grossular garnets in Wah Wah pass just off the road.

The mineral mountains  near Milford has some beautiful red spessartine garnets that look like pyrope and are found with smokey quartz.

One of my favorites is in ElyNevada. You can collect at Garnet Hill and find some very nice ones in the rhyolite. It is easy collecting and fun for the family there.




2 comments:

  1. I find garnets in my driveway gravel here in Western North Carolina. Lots of gems and minerals. Sometimes I find kyonite in the pasture, too.

    Stopping in from A-Z.

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  2. What great information and resources you have here. I would have been a geology major if I'd been younger when I went back to school.

    Happy A to Z.

    ReplyDelete