FMF - Friends of Minerals Forum, discussion and message board

[Roger Warin]

Hi,
Here is one of the basic minerals from a collection: Calcite.
In a large degree of purity (optical grade), calcite is often called Iceland spar. In Iceland, these crystals appear in basalt geodes (with zeolites).
However, now these samples come from the Cafarnaum mine, Mato Grosso, Brazil.
What do you know about this Brazilian deposit? Will has other deposits in the world of optical calcite?
Thank you.
Roger.

A stone 54.83 ct was cut out of this material.
Roger.

[Jordi Fabre]

[GneissWare]

There are lots of localities. I know of one in Inyo Co., California, and one or more in Chihuahua, Mexico.

[Josele]

In Iceland spar page in Mindat can see many locations for this pure and clear calcite variety.

Is said that some iceland spar specimens labeled as coming from Brasil actually are from La Gaiba District, Sandoval Province, Santa Cruz Department, Bolivia

I have a transparent yellowish calcite from China which can not be called Iceland spar because his color although it has the same optical properties. Can see some pics of birrefringence effects with a laser falling on different directions here: Minerales BIRREFRINGENTES

[Susan Robinson]

About 45 years ago, the zinc mines at Balmat, St. Lawrence County, New York, recovered some immense, clear calcite crystals from underground. Three large faceted stones were cut from one of the 80-lb crystals: One is just over 1,000 carats and resides at the A. E. Seaman Mineral Museum in Houghton, Michigan; one is on display at the Smithsonian; the last is on display at the New York State Museum in Albany, NY.
Susan Robinson

[Rich Loose]

Here is a link to Iceland Spar in northern New Mexico. Vince Kelly was one of my geology professors at the University of New Mexico.

https://www.minsocam.org/msa/collectors_corner/arc/nmcalcite.htm
(link normalized by FMF)

Rich Loose

[alfredo]

There was an optical calcite mine during WW2 in the Anza Borrego desert, on the border between San Diego and Imperial counties, California. The calcite was used in the manufacture of bomb sights for the air force. Our geology class at SDSU took a field trip there. One can still see cleavage fragments of calcite scattered around. (But no collecting, as this is Anza Borrego Desert State Park land, I believe.)

[Pierre Joubert]

Optical calcite was also mined at the farm Soetwater, Calvinia, Western Cape, South Africa. Duncan could possibly elaborate on this if he is following this thread.

[Duncan Miller]

Hi Pierre

You are correct. There are several calcite-bearing hydrothermal pipes intruding Karoo rocks near Calvinia. The Soetwater mine was worked in the 1960s (and possibly into the 1970s) by a privately owned US company making optical splitters for laser systems. Unfortunately I no longer can find their promotional brochure or remember the name of the company. The mine was visited quite frequently by members of the Cape Town Gem & Mineral Club until it was closed and collecting access denied by the farm owner. Initially the mine was a vertical pit that eventually was opened up downslope into a quarry. Reportedly some very large masses of optical calcite were found, measuring several metres in size.

Duncan