This is a very pretty specimen of acanthite from Guanajuato. Actually, that is incorrect, or, rather, imprecise. This is an acanthite paramorph of argentite. When this specimen formed, it was an argentite crystal and it formed at a high (to us humans) temperature. As it cooled, the crystal structure changed into that of acanthite. It makes a difference: argentite is a cubic mineral and acanthite is an monclinic mineral. If you were to analyze the way the molecules in this specimen are arranged, you would see they are monoclinic despite the exterior appearance of a (complex) cubic crystal?<BR><BR>
Confused yet? Me too. Just know this: you can't collect argentites unless you house your collection at above 177 degrees Celsius.<BR>
Sooooo, this acanthite, which reminds me of an unfinished Borg ship (for you Star Trek fans), comes from the famous silver mines in the city of Guanajuato, in the state of GUanajuato, in the country of Mexico. It is undamaged with good luster. It measures 2.2 x 2 x 1.8 cm. I used to get many of these crystals on my trips to Mexico, but the supply has both shrunk year by year, and become more and more expensive. This is a wonderful thumbnail specimen that I purchased more than 5 years ago in Guanajuato from a local miner.