Ontario Amethyst -
Ontario's Mineral Emblem
Amethyst is valued not only for its striking colour and rarity, but also for its reflective nature and its durability. Such qualities led to the selection of amethyst as Ontario's mineral emblem by the Honourable Leo Bernier, Minister of Natural Resources, on May 14, 1975. The Mineral Emblem Act received first reading in the Provincial Legislature on June 17th and Royal Assent on July 8, 1975.
Pyramid-shaped amethyst crystals.
Sample is from the Thunder Bay area.
Ministry of Northern Development, Mines and Forestry specimen and photo.
While occurring worldwide, amethyst is in rich supply along the Lake Superior's north shore near Thunder Bay. It is also found in the Bancroft and North Bay areas.
The earliest mention of amethyst near Lake Superior dates back to the 1600s, but the first large deposit was discovered in 1955 in McTavish Township just east of Thunder Bay. In the Thunder Bay area, amethyst crystals formed in cavities created during the Keweenawan faulting of the Lake Superior basin about 1.1 billion years ago. Here amethyst is found with other minerals such as pyrite, galena, sphalerite, chalcopyrite, calcite, fluorite, and native silver. Amethyst occurs as beautiful purple crystals, with some having a thin layer of reddish brown hematite trapped just beneath their surface.
Legend and Facts
Although the reasons for the striking purple hue of amethyst are now known, the original naming of this gemstone stems from Greek mythology. In the legend, the god Dionysus, enraged by an insult, vows to set his tigers upon the first mortal to cross his path. A young girl on her way to the shrine of the goddess Diana comes upon the tigers. To protect her, Diana transforms her into ‘rock crystal’ (quartz). The remorseful Dionysus pours a goblet of wine onto the crystal in offering to the girl. This gives the crystal a purple hue and the name ‘amethyst’ which derives from the Greek word meaning ‘not drunken’.
Amethyst, a variety of quartz, contains excess iron within its structure. When the atoms of iron are aligned, rather than scattered within the crystal, light passing through is seen as a purple colour. The alignment of iron is caused by the emission of low-level radiation from the surrounding rocks.
Purple amethyst crystal on a fragment of granite from the Thunder Bay area.
Ministry of Northern Development, Mines and Forestry specimen and photo.
In Ontario the six-sided purple amethyst crystals are found in thin sheetlike deposits in crevices called veins and in vugs – pockets within rock where trapped liquids and gases have created an environment suitable for crystal formation. With the growth of crystals zoning takes place – layers of different colours caused by changing compositions of the fluids that formed amethyst. Thus no two amethyst crystals are alike in colour or composition. One crystal can be uniform in colour while another can vary from a subtle shade of lavender near the crystal base, to an intense, dark purple at its point.
Decorative Design and Decor
A 22ct. ring of deep purple amethyst
from Thunder Bay Amethyst Mine Panorama.
Royal Ontario Museum specimen and photo.
Although commonly featured in jewellery settings, amethyst can also be used for a variety of decorative pieces from clocks and vases to trophies or bookends.
It is used as an ornament in its natural form or sliced through and polished, then mounted in a variety of ways that display its structure, translucence and colour.
Larger blocks of crystals have inspired many inventive designers to build monuments and fireplaces. Visitors to the mines will find a wide selection of gift items available for purchase.
Large amethyst termination beside ring;
both from Thunder Bay Amethyst Mine Panorama.
Royal Ontario Museum specimen and photo.
Mining Ontario's Amethyst
Plate of pale to dark purple amethyst on pink granite matrix
from the Pearl area.MNDMF specimen and photo.
Several amethyst mines operate near Thunder Bay, all using the surface method of mining which, with controlled blasting, fre es large blocks of rock from the ground. Miners using small hand tools to separate the crystals from the rock do the delicate work of breaking down these rock blocks. At some mines, visitors are welcome to search out their own crystals.
Ontario Amethyst Producers
Ontario Amethyst Producers are listed on the Gemstone and Mineral
Specimen Mines and Quarries page within the
Ontario Mining and
Exploration Directory
Properties of Amethyst
Colour:
- Natural amethyst ranges in colour from very pale violet to dark purple.
- The colour is caused by iron ions replacing silicon ions in quartz; the iron is then ionized with low level natural radiation.
Hardness
- Quartz (amethyst) has a hardness of 7 on Moh's* hardness scale.
* On Moh's hardness scale talc, the softest mineral, has a hardness of 1 and diamond, the hardest mineral, has a hardness of 10. Quartz at 7 will scratch a knife blade
Crystal shape
- If it grows in an unrestricted space, amethyst will form six sided prismatic crystals with pyramid-shaped ends
Fracture
- Amethyst will break into uneven or conchoidal shapes, like those found in broken glass.
Refraction
- Amethyst has double refraction*. This property helps distinguish amethyst from similar looking minerals.
* Double refraction means that light coming through an amethyst crystal will be split into two beams. This is best seen using an instrument gemologists call a refractometer.
Purple to red amethyst crystals from the Thunder Bay area. The red is due to a layer
of hematite just beneath the crystal surfaces. MNDMF specimen and photo.
Geology of Amethyst in the Thunder Bay area
Amethyst veins in the Thunder Bay area occur in parallel to subparallel vein systems. Veins strike northeast and east, parallel to major Keweenawan faults. The best amethyst crystals occur in vugs and the largest vugs occur at the intersection between the northeast and east trending faults and fractures. There is a spatial relationship of amethyst deposits north of Thunder Bay to the 060o regional unconformity/vein system that stretches from Northern Light Lake in the southwest to Kabamichigama Lake in the northeast. This regional system also hosts silver, lead and zinc mineralization.
Because, in the Thunder Bay area, amethyst formation is restricted to near-surface conditions, the amethyst occurrences are located within 50 metres of the subhorizontal unconformity between the Archean and Proterozoic rocks shown on the map and cross-section below. The unconformity has also acted as a mechanism for concentrating radioactive minerals essential in the formation of the purple colour of amethyst.
Geology map and legend of the Thunder Bay area from Geology of Ontario map 2542.
Amethyst is currently being produced in Area 1 centered on Pearl, Ontario.
Amethyst occurrences have also been found in Area 2 northeast of Nipigon.
Precambrian
Proterozoic
Keweenawan (0.9 - 1.6 billion years old)
31abcd mafic and related intrusive rocks
29ab Osler Group; mafic and felsic volcanic rocks and associated sedimentary rocks
28 Sibley Group; sedimentary rocks
Paleoproterozoic (1.6 - 2.5 billion years old)
22a Animikie Group; sedimentary rocks
Unconformity
Archean (2.5 - 3.4 billion years old)
15 massive granodiorite to granite intrusive rocks
14 diorite-monzonite-granodiorite intrusive rocks
13 muscovite-bearing granitic intrusive rocks
12 foliated tonalite intrusive rocks
11 gneissic tonalite intrusive rocks
10 mafic to ultramafic intrusive rocks
9 coarse clastic sedimentary rocks
7 sedimentary rocks
6 felsic to intermediate volcanic rocks
5 mafic to intermediate volcanic rocks
Schematic cross-section showing geologic relationships
of Archean and Proterozoicrocks north
of Lake Superior.
Figure is from Amethyst Deposits of Ontario, Geological Guidebook No. 5 by Max
Vos published by the Ontario
Mines and Minerals Division, Ministry of Northern Development and Mine.
Additional information may be obtained from the following Ministry of Northern Development, Mines and Forestry; Ontario Geological Survey publication: Garland, M.I. 1994. Amethyst in the Thunder Bay area; Ontario Geological Survey, Open File Report 5891, 197p.
For information on ordering Ontario Geological Survey publications please follow the web site link:
http://www.MNDMF.gov.on.ca/mines/ogs/ims/pub/order_e.asp
Ontario Amethyst Internet Links
Some of the web site links included below are outside the Ontario government. The host organizations are responsible for the information contained within the respective sites. These sites may not be available in French. Any specific comment or inquiries regarding these sites should be directed to the individual organization.
Ontario Amethyst Producers
MNDMF Resident Geologist - Thunder Bay South District
