LAST DAY!!! Minerals Harder Than Quartz

40 specimens of minerals have been placed in our current theme auction. The focus this week is on minerals with a
hardness greater than that of quartz. Please feel free to take a look at:

http://auction2.mineral-auctions.com

FYI, the measure of minerals hardness is generally given using Mohs Scale. This was devised in 1812 by Friedrich Mohs using 10 commonly available minerals. Because of this, it is usually easy to find the 10 reference minerals (with the possible exception of diamonds). There is a good summary to be found at:

http://www.allaboutgemstones.com/mohs_hardness_scale.html

It includes a graphical comparison to absolute hardness. The numbers refer to the ability of one mineral to scratch the surface of another. This can get confusing when some harder minerals tend to crumble (we might call them
friable), have strong cleaveages (it is easy to cleave topaz even though it is quite hard), or have different hardness in different directions (kyanite). So, have fun looking and think a bit about how you might use hardness to identify
an unknown mineral.

One interesting usage of the harder than quartz question is whether or not a mineral is suitable for use in a ring. Since quartz is a common component of dust, you might not want to choose something softer than quartz as it will get scratched over time.

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Thanks once again Keith I love these themed auctions and the information that comes along with it!

Trinity Mineral Company Auctions

Allochromatic and Idiochromatic minerals

If you know me you know that I am attracted to "new" words...

Today's Daily Jewel is inspired by the latest auction offering from Keith at Trinity Minerals mineral-auctions.com

This time around the theme is minerals colored by nickel, lead or chromium. Check them out at:

http://auction2.mineral-auctions.com

This theme was suggested by Miranda (of Dakota Matrix) and include allochromatic and idiochromatic minerals.

Idiochromatic refers to minerals whose color is set by their composition. A good example of an idiochromatic mineral is linarite which is always an intense blue color.

Allochromatic refers to minerals whose color varies based on the presence of impurities. Green grossulars are a good example as the presence of chromium in ppm levels causes the normally colorless grossular garnet to be tinted green... another maybe more familiar example is ruby which is the chromium rich variety of corundum.

Check out the auction for more on these terms...but get there soon. The Crocoite specimen pictured from the area of Dundas, Tasmania in Australia has already sold out!

Photo Info: Crocoite offered by Bill Logan - It is "an aesthetic grouping of stout parallel prismatic crystals with excellent luster and a bright orange-red color. Crocoite is one of the very few Chromate minerals considered collectable due to its vivid color. This is due to Chromium, a versatile chromaphor, which also imparts color to Ruby and Emerald. The lead content adds density and luster. This is an older specimen featuring stout blunt crystals, less fragile than more recent specimens. The featured aerial terminarion is undamaged but imperfect with accumulation of the yellow granular mineral so often seen in association with Dundas material. The accessory crystals do show some conchoidal fractures, but overall it displays beautifully."