Amethyst – February Birthstone

Everyone likes the color purple and mineral collectors like shiny crystal surfaces and perfect terminations.  Therefore, is it any wonder that amethyst attracts attention?   Whether it is spotted in a 2” miniature specimen off matrix, filling a small geode, or covering a huge Brazilian crystal cathedral, eyes are always drawn to the splendor exhibited by a fine amethyst piece.  Given its appeal, is it any surprise that amethyst is the February birthstone?

Quartz is hard, clear and common.  Amethyst is hard, clear, not so common, and purple!  One can enjoy amethyst without understanding the rather complex reason behind its color, but it is also interesting to know a little about the minerals in your collection.  While complex in detail, it can be generally stated that it takes two very distinct properties to produce the distinct purple hue in amethyst.  First, a small amount of iron must replace a few of the silicon atoms in the center of the SiO4 tetrahedrons upon which quartz is constructed.  Second, the host rock must contain sufficient radioactive sources to emit gamma rays that over time irradiate the iron (Akhaven, 2012).  This will cause the ferric iron (Fe+3) to jump to the unusual oxidation state of Fe+4.  In this state it does not take much iron to impart a purple color and amethyst is born!

Amethyst has been a favorite for countries issuing mineral stamps.  Uruguay and Kenya issued amethyst stamps in 1971 and 1974 respectively.

Amethyst has been a favorite for countries issuing mineral stamps. Uruguay and Kenya issued amethyst stamps in 1971 and 1974 respectively.

There are just about as many textural ways for amethyst to manifest itself as there are localities where it occurs.  The very deep purple color of amethyst from Uruguay is probably due to the uniform distribution of iron and the strong presence of radioactive elements in the host basalt.  In 1971, Uruguay featured their famous amethyst on a stamp (see above).  Brazilian amethyst has a similar origin, hosted in fractures and vugs in basaltic lava flows, but can generally be distinguished by a slightly paler purple color.

Much of the world’s amethyst grows in fractures and vugs in volcanic rocks.  These vugs can be regularly shaped geodes, or very large elongated “caverns” such as the famous Brazilian “amethyst cathedrals”.

Brazilian amethyst cathedrals, like that on the right, are highly prized pieces and are often used as raffle prizes at mineral events.  The cathedral pictured here was the grand raffle prize for the 2010 St. Lawrence County Club show in upstate New York.

Brazilian amethyst cathedrals, like that on the right, are highly prized pieces and are often used as raffle prizes at mineral events. The cathedral pictured here was the grand raffle prize for the 2010 St. Lawrence County Club show in upstate New York.

Another prized form of natural amethyst is the specter.  Quartz can grow in stages and sometimes smaller crystals are overgrown by larger ones.  When the larger overgrowth is amethyst an exquisite piece is born.

The piece on the left is almost 2” tall and is from John Betts online mineral museum.  Switzerland honored the International Year of Crystallography in 2014 by placing a very nice amethyst specter on a postage stamp.

The piece on the left is almost 2” tall and is from John Betts online mineral museum. Switzerland honored the International Year of Crystallography in 2014 by placing a very nice amethyst specter on a postage stamp.

Sometimes, there is so much iron incorporated into the quartz as it grows that the unradiated sample is red from microscopic hematite inclusions.

Combinations of red colored quartz with amethyst can be particularly appealing as shown by the piece on the 1982 Germany stamp.  The internal hematite in  the Thunder Bay, Ontario amethyst piece on the right imparts a reddish color to the otherwise purple mineral.

Combinations of red colored quartz with amethyst can be particularly appealing as shown by the piece on the 1982 Germany stamp. The internal hematite in the Thunder Bay, Ontario amethyst piece on the right imparts a reddish color to the otherwise purple mineral.

In recent years, WCGMC has collected amethyst in Prospect, Virginia and in Thunder Bay, Ontario.  The Schuffin’s Acres Farm (previously Simpson Amethyst Mine) in Virginia exploits a mineralized fault zone where amethyst tips and clusters are recovered out of a weathering fault zone (Jacquot, 2014).

Virginia amethyst: Linda Schmidtgall dug the pieces in the left picture on a March 2014 WCGMC trip.  Those depicted in the center and the right are from Mindat and Youtube videos on the location, respectively.

Virginia amethyst: Linda Schmidtgall dug the pieces in the left picture on a March 2014 WCGMC trip. Those depicted in the center and the right are from Mindat and Youtube videos on the location, respectively.

Amethyst is encountered in fractured and brecciated volcanics that covered the U.S.midcontinent region about 1.1 Billion years ago.  The Amethyst Mine Panorama (a fee collecting site in Thunder Bay, Ontario reports a 60-70 year supply of amethyst, probably because Linda Schmidtgall got her supply at the Blue Point Mine in August 2013.

Amethyst in brecciated rock, Thunder Bay, Ontario.

Amethyst in brecciated rock, Thunder Bay, Ontario.

No discussion of amethyst is complete without reviewing its various lapidary uses and its quality as a gemstone.  From simple polished stones, to banded cabochons, and, of course to faceted gemstones, amethyst is always finding its way into the project list of anyone working with stone.

WCGMC has quite a collection of lapidary amethyst.  The sphere on the left was awarded to a lucky raffle winner at GemFest 2015.  Ed Smith has faceted some gems (upper middle) and someone will get a chance to carve up polished sections from the layered amethyst vein (lower middle).  Purple hearts on the right only lack a jewelry chain.

WCGMC has quite a collection of lapidary amethyst. The sphere on the left was awarded to a lucky raffle winner at GemFest 2015. Ed Smith has faceted some gems (upper middle) and someone will get a chance to carve up polished sections from the layered amethyst vein (lower middle). Purple hearts on the right only lack a jewelry chain.

References:

Akhaven, A. C., 2012, The Quartz Page: Amethyst, website:  http://www.quartzpage.de/amethyst.html

Amethyst Mine Panorama website:  http://www.amethystmine.com/

Jacquot, R., 2014, Scufflin Acres, Virginia’s Earth Shaking Amethyst, v. 1. #2, p. 55

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