Tuesday, February 17, 2009


Sapphire vermiculite schist from Palmer Canyon. This sample is formed of an estimated 40% pink sapphire and is just one of dozens of samples collected by the author that had from 20 to 50% corundum (ruby and sapphire) by volume.
CORUNDUM (Al2O3)  Characteristics & Habit. Corundum (H=9) is the second hardest naturally occurring mineral: only diamond is harder. As a result, gemstones made from corundum are durable. Raw corundum occurs as barrel-shaped hexagonal prisms with rough, rounded surfaces often exhibiting distinct parting. Because of good rhombohedral and basal parting corundum prisms often terminate at basal pinicoids & display striations due to repeated twinning.

Corundum exhibits a variety of colors including gray, grayish green, blue, pink, brown, red & purple. Some corundum is used to produce extraordinary gemstones. Ruby is the deep pigeon’s-blood red translucent to transparent variety of corundum with adamantine luster and sapphire includes all other colors.

Hexagonal (6-sided) ruby in mica schist.

It will display a striking adamantine to vitreous luster noticeable in faceted gemstones. High specific gravity (4 to 4.1) is favorable for its concentration in black sand concentrates in streams. During sampling in the central Laramie Range, we recovered tiny rubies and sapphires in several sample concentrates in that region, suggesting that several corundum deposits remain to be discovered.

Palmer Canyon ruby mounted in necklace (photo courtesy of Chuck Mabarak) & showing cleavage (right - note the distinct lines in the gemstone).

THE CORUNDUM GEMSTONES include a variety of colors including:
Red Ruby
Cornflower Blue Sapphire
Colorless Leuco-sapphire
Light bluish-green Oriental Aquamarine
Green Oriental Emerald
Yellow-Green Oriental Chrysolite
Yellow Oriental Topaz
Aurora Red Oriental Hyacinth
Violet Oriental Amethyst

Occurrence. Corundum, a high-pressure aluminum oxide, is found with silica-poor aluminum-rich metamorphic rocks in areas of metapelite. Metapelite is the key to finding many gemstones in Colorado, Montana & Wyoming as discussed in my book (in preparation) The Geology of World Gemstone Deposits. Some discussions on these rocks are found in my new book on GEMSTONES in Wyoming.

Ruby with cleavage from
undisclosed location in WY
Metapelite may contain a variety of alumino-silicate porphyroblasts such as mica, kyanite, sillimanite, andalusite, vermiculite & cordierite. The corundum itself is typically found in vermiculite schist and aluminum-rich serpentinites. Vermiculite schist is considered an alteration product of a former metapelite in which metapelite was desilicated leaving mica-rich rock known as vermiculite schist or glimmerite schist. After noting the close association of vermiculite & ruby, I discovered several more ruby deposits in Wyoming. This was also true of iolite and pelitic schist. Using geology proved to be extremely valuable.

Twinned corundum with
distinct hexagonal cross-section
Small, twinned corundum from Wyoming. Note the 6-sided crystal prism that is bounded by pinacoids (flat surfaces).

Localities. Corundum has been found at a number of places in Wyoming. Wyoming could easily develop a major ruby and sapphire industry along with many other commodities - such as diamond, gold, palladium, rare earths, iolite, labradorite, copper, zinc and silver - but its political regime with the US Forest Service have worked for more than 30 years to withdraw nearly all non-energy mineral resources from public lands - something that should be considered illegal. Over the years, we provided evidence for major and world-class mineral deposits and several companies found significant base metal deposits, only to find government interference at every level.

One interesting locality lies northwest of Jeffrey City, known as the Red Dwarf deposit (sections 13 and 24, T30N, R93W), was investigated by me several years ago. The deposit consists of corundum gneiss & schist with a 5,000 foot strike length with widths of 20 to 50 feet. The rock has 1 to 10% corundum porphyroblasts encased in zoisite-fuchsite reaction rims and considerable fuchsite and zoisite pseudomorphs after corundum. Where found, some of corundum is translucent with good color.

Large ruby-zoisite porphyroblast collected at the Red Dwarf deposit by J. David Love of the US Geological Survey. Much of this giant ruby was replaced by zoisite, but some excellent pigeon’s blood red ruby remains untouched. Prior to replacement, this specimen would have been one of the largest rubies in the world. It also suggests that large rubies remain to be found at the Red Dwarf.

The corundum may be light purplish-pink, lavender, to reddish-purple, and range from millimeter size to more than two inches across. Some gem-quality corundum was found in the past and partially replaced specimens provide evidence for rubies of five inches (or more) in length and more than 2 inches in diameter.

A nearby serpentinite discovered west of the ruby schist contains tiny (millimeter size), light-blue, translucent to opaque corundum. Locally, the serpentinite has 20 to 40% corundum.

Ruby enclosed in reaction rim found by Eric Hausel at Red
Dwarf deposit in Granite Mountains.
At another deposit known as the Abernathy deposit (section 26, T30N, R96W) near Sweetwater Station, pale-blue and white corundum is found in mica schist. The corundum is abundant and occurs as one-inch diameter nodules in the schist.

Corundum is also associated with vermiculite schist (glimmerite) west of Wheatland in Palmer Canyon. This deposit (N/2 Section 18, T24N, R70W) is associated with kyanite, cordierite, and sillimanite schist and gneiss. The corundum forms small, hexagonal, pink, red and white grains from about 0.1 to 0.3 inch across. Many grains have well-developed parting which limits the size of facetable material. Even so, significant percentages have excellent color, and are transparent to translucent (Personal field notes, 1997). Locally, the schist may contain >20% corundum. Small amounts of corundum have also been identified at the Grizzly Creek iolite (cordierite) deposit to the south and other localities to the north.

Gem-quality 8 to 12 carat pink sapphire (left) & sapphire-kyanite schist from Palmer Canyon (right).

Some corundum was identified in vermiculite schist in the Platte River Valley between the Medicine Bow and Sierra Madre Mountains. Another notable corundum locality is in the Big Sandy opening along the southern margin of the Wind River Mountains, where hundreds of corundum crystals weighing up to 90 carats have been collected from Squaw Creek by prospectors (Russ and Joe Sims, personal communication). The source of this corundum remains undiscovered. Some nearby ruby schist float was found (B.F. Frost, Personal communication) suggesting that a potentially significant ruby deposit awaits discovery.

Photos of ruby, sapphire and iolite (blue) gems and raw material from Wyoming. Note the presence of parting (cleavage in some specimens - parallel fractures) and the 6-sided characteristic of the corundum.

Find more information about dozens of rubies and sapphire localities and methods I used to find several of these deposits from my book. See you on the outcrop - the GemHunter.

Below - Raw translucent pink sapphire from Palmer Canyon. Below right -  faceted pink sapphires & blue iolites from Palmer Canyon, & Below far right - large raw ruby from the Rattlesnake Hills, Wyoming. In addition to these stones, the author was following rubies near the Big Sandy opening in the Wind River Mountains, the Rattlesnake Hills, Barlow Gap, the Sierra Madre, the central Laramie Range & the Saratoga valley.