Saturday, August 15, 2009
Friday, August 14, 2009
Wednesday, August 12, 2009
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:
FYI, the measure of minerals hardness is generally given using Mohs Scale. This was devised in 1812 by 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:
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.
Thanks once again Keith I love these themed auctions and the information that comes along with it!