CORUNDUM: A VISUAL EXPERIENCE

CORUNDUM: A VISUAL

EXPERIENCE


Corundum is a special mineral, not only because of its economic importance (in gem form it is ruby or sapphire; and emery abrasive is a sub-gem form), but also because of its diversity of colors, forms, associations, and source localities which makes it uniquely attractive to collectors. The specimens illustrated here are selected from our research/display collection to reflect this diversity. (Click on thumbnail for larger photo.)

In its pure form, corundum is a transparent, colorless form of aluminum oxide, Al2O3. It crystallizes in the hexagonal subsystem of the trigonal system. Hexagonal prisms (such as the Kenyan sapphire on the left) and pyramidal modifications (Burma, left and Sri Lanka, right) are characteristic forms.

Perhaps the most attractive are the bipyramids such as the classic Sri Lankan "geuda" crystal on the left. On the right are two Brazilian hex prisms and a pyramidal cluster from the original Kashmir alluvials - note white kaolin residue still attached.

Hexagonal prismatic crystals occur in a variety of proportions: "elongated", "prismatic" (I know, redundant), "tabular", and "wafer", for example. Those to the right also show some of the color variety. They are (left to right) from "Zoutspansburg", South Africa; Karnataka, India; Madagascar; Dat Taw Mine, Mogok Stone Tract, Burma; and Tanzania.


		Some of the finest wafer crystals come from the United States; and one of the finest of these (left) is this 6.62 carat flawless gem from the Vortex Mine, Yogo Gulch, Montana. The tabular ruby on the right is from the Dat Taw Mine, Mogok Stone Tract, Burma.

Lateral faces of corundum crystals are often "smooth" (Madagascar, left), "striated" (Burma, right), or "layered" (India, second photo below). Extreme layering can produce lovely, rose-like clusters (Russia, below far left). Terminal faces can be "smooth" (Mozambique, left center), but are often "layered" (Burma, center, and India right center), or distinctively "triangulated" (Pakistan or Afghanistan, far right).

Twins are common from some localities, and produce specimens that the "crystal killers" (faceters) hate but collectors love. The Vietnamese (far left) is a good example of "contact twinning". Following are another contact twin from Afghanistan (illustrated in Lapis Magazine, ex coll. Andreas Weerth), "interpenetrant" twins from India and Transvaal, and a neat, floppy-eared "puppy dog" twin from Viet Nam.

When several crystals grow together to form clusters, the effects can be striking. The one on the far left is known as "The Bird Nest", and is from Nepal. Near left piece is from Somalia. On the right is the "Ugandan Road Kill Pigeon", which may actually be from across the border in Kenya..

Below: two clusters from Viet Nam ("The Rocket Ship" and a pyramidal cluster), one from Sri Lanka ("The Goldfish"), and two from Tanzania (Longido and Morogoro respectiely).

Bottom Row: Ilmen Mountains, Russia, Nepal (Chumar Mine), Spider Mountain (Mogok, Burma), and two other Mogok specimens.

Polycrystalline or even massive corundum can be interesting, as these three specimens from the vicinity of Franklin, North Carolina portray. All of these (collected before 1850) may have come from Corundum Hill, just outside Franklin, which was mined for emery (they ground this stuff up)!

Many corundums are found in river gravels. Perhaps the most famous of these are the Montana alluvial deposits (top left photo). Left Photo: The seven sapphires illustrated on the far left from Rock Creek (Gem Mountain) and and the four on the right from Dry Cottonwood Creek were gifts of Marc Bielenberg to Louis Zara. The hot pink in the upper center was given to me by Ben Duffey. Bottom left photo indicates the variety of colorful sapphires that can be recovered from the Umba Valley, Tanzania alluvial deposits - these select specimens show little or no abrasion

On the top right above are two waterworn specimens from the Mano River which runs along the borders of Guinea, Liberia, and Sierra Leone in West Africa. Below them is a ruby cobble found in the gold dredge tailings of Alder Gulch, near Virginia City, Montana.


			Corundum occurs in nature with (or after) a variety of other minerals. Calcite is the most common. Note how the snow white color contrasts with the brilliant red of the Viet Namese ruby (far left). The second photo shows a 2-1/4" long gem ruby from Afghanistan in a contact between grey and white calcite. On the right is very rare "Ruby Cave", Burma specimen, which apparently formed in nepheline calcite.

Left to right: nepheline provides the matrix for a historic Sri Lankan specimen, rubies in syenite from Viet Nam, and a remarkable large fist cluster of gem rubies in zoisite from the classic Longido, Tanzania locality.

These three American specimens are unusual. First is "Barney, the Dinosaur" (rubies in smaragdite) from Chunky Gal Mountain, North Carolina. Second is a nodule of blue/white corundum altering to margarite mica from Franklin, North Carolina. Third is a Yogo Gulch, Montana sapphire in lamprophyre(?) matrix - note the rock is not green!

Here are some true rarities - in fact, in our experience they are unique! The first is ruby with fossils - crystallized in a mud pocket with opalized snail shells; from the John Saul Mine in Kenya (given by John Saul to Cal Graeber). The second is a detail of an unusually aesthetic association of ruby with diopside, from Tanzania somewhere. The third shows a trio of pink elongated doubly terminated prisms , allegedly from Morogoro, Tanzania.

Some corundum localities are well known for the gems they produce - and among these, Burma and Kashmir set the standard against which all gem rubies and sapphires are measured. However, as a mineral collector, I find others just as attractive (and often more affordable)! To illustrate the geographical variation, we conclude this photoessay with some armchair travel. See GALLERY pages for more photos and information.

Karnataka (Mysore) Province, India has several holes in the ground that have produced remarkable, large ruby crystals, ranging from brownish to purplish red. The ones pictured to the right weigh up to 20 pounds.

Other Karnataka localities produced "watermelon ruby" encapsulated in blue zoisite rind (often misidentified as corundum or kyanite -far left), doubly terminated rubies in gneiss (near left) and huge blocks of massive ruby/sapphire corundum suitable for carvings such as this 45-lb. "Ganesha" (right). (Carving is property of Anil Dholakia.)

		Nepal is not a large producer of corundums, but look at these! The cluster on the left (2 views), from the Chumar Mine, Ganesh Himal, is one F. John Barlow described in a personal letter: "This, without question, is the finest ruby crystal group ... and I don't believe (it) will ever be topped." The details on the right show unique "shark fin" projection, green fuchsite mica, and unique "chain" of crystals seen on several of the "original" ruby specimens (ca. 1981) from the Chumar Mine. The pale blue sapphire in matrix is from recent artisanal operations in the northeastern Taplejung region.

European localities are not known as major gem sources, but occasionally they produce important mineral specimens. The tabular ruby on the left, from the Sivec Mine near Prilep, Macedonia, weighs over four pounds, and is apparently the largest ever found at the site. Center photo is one of my favorite crystals from the Ilmen Mountains, Russia. On the right is a superb cluster of terminated rubies in gneiss from the Klegaassen Pegmatites near Arendal, Norway.

Burma (Myanmar) is arguably the source of not only the finest gems but also the most interesting and varied mineral specimens. Top: mass of bipyramids from Spider Mountain, Mong Hsu cluster, extremely cavernous complex crystal from Dattaw Mine. Bottom: Pastel striated crystal from Ka Baing, rare brown gemmy crystal from Mogok, pair of large gem rubies from Kuat Sar Taung (Mogok).

So, I hope you have enjoyed this look at specimens from our collection of this most remarkable mineral. In all, there are over 2,300 catalogued specimens and lots, including many of types or from localities not illustrated here. Please e-mail me at collector@corunduminium.com if you are interested in anything related you do not see here. I shall try to reply to each query as soon as possible, either personally or by posting the info on the "What's New" page of this website. This is a one horse show; so please be patient.

Will Heierman

(Author's Note: As I am a mineral collector not trained as a geologist or mineralogist, there may be technical errors or more precise ways of saying things that should be brought to my attention. If you see one, please e-mail me at webmaster@corunduminium.com.)