When prospecting for ruby and sapphire - remember these are 'aluminum oxides' that have been subjected to high-pressure and temperature equivalent to what geologists refer to as 'amphibolite facies metamorphism'. Sounds complicated? Just remember you are prospecting for rocks that are very aluminum rich - such as mica schists, serpentinites, aluminum-rich lamprophyres, anorthosites and vermiculite schists.
Characteristic cross-sectional crystal habit of corundum (ruby & sapphire). Note the 6-sided hexagonal shape of corundum.
These rocks need to have been subjected to amphibolite grade metamorphism (high pressures and temperatures). Thus you should be looking in regions of mountaineous terrains or continental cratons that have extensive regions of metamorphic rocks with some amphibole. Take for instance, most mountain ranges in Wyoming and Montana. Simply by searching for vermiculite schist (glimmerite) I discovered six new ruby and sapphire deposits. So check your local geological survey for old studies on vermiculite. It was once an important commodity in the 1930s and 1940s needed for insulation. Not all have gemstones, but a significant number in the mountain regions (and gneissic cratons) will have them.
So how do you recognize a ruby in the raw? It will form an hexagonal prism often with distinct cleavage.
Hexagonal prism in vermiculite schist from Palmer Canyon, Wyoming. This pink sapphire that I recovered is estimated to be 30 to 40 carats in weight.
Rubies and sapphires bring visions of incredible value - but possibly none more than a Burmese ruby of 15.97 carats that sold at a Sotheby’s auction for US$3.63 million ($227,301/carat). More recently in 2005, Christie’s of New York sold a near perfect 8.01-carat Burmese ruby with strong fluorescence for US$2.2 million at a record price for a ruby (US$274,656/carat)! And a 62-carat royal blue rectangular cut sapphire was purchased for $2.8 million ($45,000/carat). Rubies are more valuable than sapphires, even though the are the same mineral.
The schist on the right is a ruby-sapphire vermiculite schist from Wyoming with as much as 5 to 10% corundum! After I found this and another ruby vermiculite schist in Wyoming, I realized there was likely a connection between these aluminous schists and ruby and sapphire. Next, I went to the archives and found an old booklet on Vermiculite Deposits of Wyoming and began visiting these one by one (in the 1930s and 1940s, vermiculite was a hot commodity for use in insulation). Sure enough, there was a connection. At least 6 Wyoming deposits had ruby and/or sapphire that had been completely overlooked by the earlier geologists. So, if you would like some rubies, go to your local State Geological Survey and see if they have any old publications on vermiculite. In other countries, vermiculite is sometimes referred to as glimmerite.
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 or cleavage. 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. With 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
Cornflower Blue Sapphire
Colorless Leuco-sapphireLight bluish-green Oriental Aquamarine
Green Oriental EmeraldYellow-Green Oriental Chrysolite
Yellow Oriental TopazAurora Red Oriental Hyacinth
Violet Oriental Amethyst
Poor quality, 5-carat ruby with distinct cleavage seen on the upper surface of the faceted stone collected in Wyoming.
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.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.
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).
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 (and other gemstones), look for areas with abundant mica schists or rare lamprophyres! 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 ruby deposits in Wyoming is I paid attention to the mineral habit (not all geologists can recognize ruby, in fact, we had one geologist at the Wyoming Geological Survey 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, 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 barren!
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.
Corundum from the Rattlesnake Hills, Wyoming, near 1981 gold discovery. This corundum, would be known as an Oriental Amethyst.