Ontario Amethyst Deposits (gems, gemstones, rocks, minerals and rockhounding)
June 27, 2006 by rockwatching
IMG_2124, originally uploaded by Mic2006.
At its finest this wonderful purple gem is a rich, fathomless violet frozen in stone. It was a color most valued by Roman nobility and until the latter half of the 18th century, was considered to be amongst the most precious of jewels. With the discovery of the vast Brazillian deposits the purple gems’s value was diminished with abundance.
Bishops of the Church of England wore the stone as a symbol of sobriety. This was widely believed to be one of this gem’s powers. In older times a bear carved into amethyst was said to keep the posessor from falling prey to demons and the wine drenched Greek celebrant clutched a crystal beneath his robe to ensure a rapid, painless return from drunkenness.
There is a strip of highway over the top of Lake Superior that is tinted mauve for the quantity of that mineral in the rock thereabouts. Just outside Thunder Bay there are numerous amethyst mines, some at which you can collect your own wonderful specimens.
Amethyst is a variety of quartz though its velvety hue is attributable to the replacement of some tiny amount of silicon within its atomic structure by iron. With a little radiation the gem darkens to purple. When packed in iron filings and heated it mellows to the deep gold of citrine. Today, hardly a citrine on the market has not been altered in this way.
Geologically speaking, the occurence of amethyst along the west shore of Lake Superior is quite predictable. It is an environment whereby the lake’s sedimentary basin changes to the hard igneous rock of the Canadian Shield. The gem usually can be found along the contact between the Pre Cambrian Granite and the overlying Sibley layer.
By the late 1800’s Ontario had a thriving local trade in amethyst, The vast majority of the deposits were discovered in the search for silver, copper and zinc. These base metals are known to be frequently associated with amethyst bearing fissures. The north-western shore of Lake Superior truly acheived supremacy as a gem location with the opening of the Thunder Bay Amethyst Mine in 1967.
A most recognizeable characteristic of the Thunder Bay Amethyst is its distinct color zoning. If the stone is cut diagonal to the length of the natural crystal prism it will display a chevron pattern; an intermeshing of coloured triangles with colorless stone. It is a result of crystal twinning, an idea supported by the appearance of interferance figures when the stone is examined in polarized light.
In the accompanying photo a rather healthy stone is examined. Historically the finest specimens were said to come from the Ural mountains - Catherine the Great was said to have amassed a vast collection of these gems. To this very day the designation of a gem as “A Siberian Stone” implies that it is of the finest color.
IF UP NEAR THUNDER BAY CONSIDER VISITING THE BOULDER CREEK AMETHYST MINE (45 minutes east of Thunder Bay). It has a great orange vein with watery wine red crystals or shocking purple clusters. Here you pay only for what you keep and the site is open May - October, (by appointment only).
