Sunday, September 14, 2014

Mineral of the Day: Fluorite

Fluorite is a popular mineral for collectors, since it is relatively common and inexpensive, and can be found in large, showy crystals of many shades and colors.

Frequently cubic-shaped, and blue, purple, green or yellows [though it can be found in every color of the rainbow, less commonly]. It is frequently found alongside minerals such as calcite, dolomite, galena, and sphalerite.

Some fluorite will fluoresce beautifully under UV light [as the name might suggest].

Some fluorite will even fluoresce in sunlight!

Care should be taken to keep specimens stored out of direct sunlight, as the color may fade, and it should not be stored in water, as this may also damage the specimen.

Tuesday, August 26, 2014

Fossil shell geodes

Partial fossil geode from Rio Dell, California
Ever found a fossilized shell that broke open and revealed hundreds of bright yellow crystals growing inside it, like a tiny geode?

They're usually calcite crystals that grew inside the hollow of the shell during the fossilization process -- since fossils are frequently preserved by calcite, there's an abundance of the mineral around to create the crystals.

The one above I found at Rio Dell, California -- I saw quite a few of broken ones, and probably some of my nice complete fossils have crystal vugs within them as well, although I haven't wanted to break them open and find out!

Tuesday, August 19, 2014

Mineral of the Day: Aquamarine

Aquamarine is the blue variety of the gemstone beryl, which comes in a number of different colors [Green is emeralds, golden is heliodor, colorless is goshenite, pink is morganite, and red is, well, red beryl]. The coloration differences are caused by impurities within the beryl.

Aquamarine is probably the most common, and can be found in most beryl-bearing localities. That isn't to say that it's all over the place, but it's a fairly accessible gemstone to buy. Crystals from Brazil and Pakistan are usually inexpensive, although one must be aware that they have often been irradiated to enhance the blue coloration.

Tuesday, August 12, 2014

Mystery mineral

I ran across these photos while I was cleaning out an old hard drive. Some years back, I had a job sorting and identifying a bunch of specimens that had been donated to the local college, and these were among them.

I never could figure out what they were. They're very heavy and definitely metallic, with a grayish streak. Anyone got ideas?

Saturday, July 26, 2014

Mineral of the Day: Dogtooth Calcite

Calcite is one of those minerals that can be baffling to a beginning collector, due to its myriad of different forms and colors. But it is a mineral well worth knowing -- fairly common and usually inexpensive yet lovely.

The calcite here is what is often know as "dogtooth" calcite after the shape of the crystals. The reddish color in this case comes from inclusions of hematite.

This particular specimen is from Santa Eulalia, Chihuahua, Mexico.