A GUIDE TO FINDING GEMSTONES & GOLD

Corundum is the second hardest naturally occurring mineral: only diamond is harder (this is not quite true - there is another extremely rare mineral known as lonsdailite that is even harder than diamond) (Erlich and Hausel, 2002). Corundum is found as barrel-shaped hexagonal (6-sided) prisms with rough, rounded surfaces often exhibiting distinct parting. Because of good rhombohedral & basal parting corundum prisms often terminate at basal pinicoids (flat surfaces) & display striations due to repeated twinning.

Corundum comes in a variety of colors including gray, grayish green, blue, pink, brown, red & purple. Some is used to produce extraordinary gemstones. Ruby is the deep pigeon’s-blood red translucent to transparent variety of corundum with adamantine luster & sapphire includes all other colors. Corundum displays a striking adamantine to vitreous luster noticeable in faceted gemstones. In that it has high specific gravity (4 to 4.1) it will concentrate in black sands in streams, where it can be panned with a gold pan (similar to gold). During sampling in the central Laramie Range of Wyoming, my research group recovered tiny rubies and sapphires in several sample concentrates, suggesting that several corundum deposits remain to be discovered (get a copy of that old report, and follow up the locations of the samples sites particularly since no one has to my knowledge - Hausel and others, 1988).

Palmer Canyon rubies mounted in necklace (photo courtesy of Chuck Mabarak) and showing cleavage (parallel lines in the mineral).





THE CORUNDUM GEMSTONES
COLOR                  VARIETY
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

Corundum, a high-pressure aluminum oxide, is found with silica-poor aluminum-rich metamorphic rocks in areas with abundant metapelite (mica-rich rocks). Such metapelite may contain a variety of alumino-silicate porphyroblasts such as mica, kyanite, garnet, sillimanite, andalusite, vermiculite & cordierite. The corundum itself is typically found in vermiculite schist & 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 I realized there was a close association of vermiculite with ruby, I discovered several ruby deposits in Wyoming. This was also true of iolite (water sapphire) & pelitic schist. Using geology proved to be valuable.

Corundum has been found at a number of places in Wyoming. One locality 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. I mapped 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 & considerable fuchsite (green mica) and zoisite pseudomorphs after corundum. Where found, some of corunudum 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 ruby remains untouched. Prior to replacement, this specimen would have been one of the largest rubies in the world. It also suggests that very large rubies may be found at the Red Dwarf, particularly if anyone ever digs with a backhoe.

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 & partially replaced specimens provide evidence for rubies of five inches (or more) in length & more than 2 inches in diameter in this area.

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

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) also has gem kyanite, cordierite & sillimanite schist & gneiss. The corundum forms small, hexagonal, pink, red & 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 & 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 & other localities to the north (Hausel & Sutherland, 2000).

Gem-quality 12-ct 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 the Big Sandy opening along the southern margin of the Wind River Mountains, where hundreds of corundum crystals weighing up to 90 carats were collected from Squaw Creek by prospectors (Russ and Joe Sims). The source of this corundum remains undiscovered. Some nearby ruby schist float was found with gem-quality ruby (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.

 HOW TO FIND RUBY & SAPPHIRE

To find ruby & sapphire, first don't forget who told you all this. You don't want karma to look unfavorably at you. So share your discovery with me!  Get familiar with the characteristics of the mineral (see my 2009 Gem Book). In the rough, ruby & sapphire (corundum) form rod-like prisms much of the time. These are 6-sided. They are often found in metamorphic rocks rich in mica, notably vermiculites (hope you are now seeing this connection). They are sometimes found in skarns (altered limestone) and rarely in lamprophyres.  How I found six different ruby deposits in Wyoming is I paid attention to the mineral habit (not all geologists can recognize ruby, in fact, we had one person at the Wyoming Geological Survey (who unfortunately was harassed to death) who picked up a rock with about 20% ruby but misidentified it as garnet). He was a very good geologist, but just made a mistake on identification which is easy to do. After I realized there was a close association with ruby & vermiculite (Hausel, W.D., Gemstones of the World and their Geological Environments, in preparation), all I did was go get a copy of an old report on Vermiculite Deposits of Wyoming & started visiting each site (until I was also harassed) & discovered ruby in about 30% of these deposits!  So search your local literature for corundum, vermiculite, skarns and lamprophyres and soon you may become a ruby & sapphire barron (don't forget me)!

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.