At first glance, rainbow calcite makes you feel like someone slipped you a Mickey Finn. While it is dazzling your mind, there is the nagging thought you should have your vision checked. Looking into an otherwise colorless gem, you see flashes of spectral color running closely parallel, resembling double images in a 3-D comic that don’t converge until you put on special glasses. Equally disorienting, facet edges seem stuporously out of focus.
A few seconds later, when you’ve adjusted to the paranormal aesthetics of rainbow calcite, you realize that it makes perhaps the most striking first impression of any phenomenon gem.
Not bad for a stone with a hardness of 3 on the Mohs scale and a pronounced cleavage (the tendency of crystals to break) in three directions. Rainbow calcite is too fragile for jewelry and nightmare to cut, the ultimate lock-but-don’t-touch gem.
Yet no other stone compensates so spectacularly for its many handicaps. Hence rainbow calcite is among the five most popular collector gems in the world. Or, more to the point, it is among the five most coveted collector gems because there is a long waiting list for large, flawless specimens of this stone. And no wonder. Prices range from $8 to $20 per carat, depending on size and quality, and reflect calcite’s status as one of the most common minerals on earth. However, finding the right crystals for rainbow stones is an often fruitless treasure hunt.
Special Effects
To get the rainbow effect in calcite, you need what gemologists call “twinning,” the intergrowth of two or more crystals during a gem’s formation. Since calcite is doubly refractive, it is already prone to a light disturbance known as “birefringence” (the splitting of single light rays into two rays that travel at different speeds and make facets appear blurry). But intergrowths wreak even more havoc on light rays.
Fortunately for collectors, that havoc manifests itself as spectral color flashes when stones are rotated in the hand. The more intergrowths, the deeper the color of these flashes if —and this is a big if—the twinning planes are cut at proper angles to the table. Since proper cutting means loss of at least 85% of the rough, some cutters cutters sacrifice beauty for bulk. That’s a no-no.
The temptation to cut for size is understandable since rainbow calcite usually looks its best in stones over 50 carats. Hence collectors always clamor for mammoth sizes. The trouble is that very few twinned calcite crystals are clean enough to yield ultra-large stones. One of the foremost collectors of rainbow calcite, Harold Dibble of Angola, N.Y., owns two exceptionally beautiful stones of 1,077 and 1,830 carats, respectively. The latter of these behemoths is showcased on the page opposite. Many who saw it exhibited at the Tucson Gem and Mineral Show in February 1992 rank it as the world’s finest faceted rainbow calcite.
Incredibly, Dibble’s stone and two more of the four known flawless 1,000-carat-plus rainbow calcites were cut from the same extraordinary crystal—by the same man. The saga of this crystal and the man who cut its best sections is as dramatic as the far more familiar saga of the 125-carat Jonker diamond cut by Lazare Kaplan in 1936. Yet until now, the story of this gigantic crystal, one of the wonders of modern gemology, has never been fully told.
Gone Fishing
If you ask collectors to name the best source of rainbow calcite, they will invariably answer Belmont, N.Y., 100 or so miles north of Syracuse and home of the St. Joe’s Zinc Mine, owned by the Zinc Corp. of America. For decades, miners there were allowed to retrieve fine calcite crystals and mineral specimens and sell them to dealers to supplement their incomes.
Then, in 1968, miner Percy Caswell hit upon a calcite crystal 600 feet underground which for weight alone would have been worthy of mention in the “Guinness Book of World Records.” Little did he realize that it would prove as peerless in grandeur as girth. Concerned only with the physical enormousness of the find, Caswell’s crew ceased all other work to recover the crystal. After a week of careful digging, they hoisted the crystal to the surface where it weighed in at an astonishing 2,000 pounds. But the brass at Zinc Corp. wasn’t impressed. To the contrary, management was so miffed at the miners for spending a week extracting the crystal that it nixed any further exploring for calcite—a ban which is still in effect at the St. Joe Mine, although the company is well aware miners occasionally sneak crystals out.
Meanwhile, the miners divvied up the stone into large chunks and sold them to dealers. For more than a decade, portions of the crystal sat on shelves, mantelpieces and window sills. Although lapidaries who studied some of the crystal’s heftier sections noticed they were rich in twine and flawless areas, calcite’s extreme softness and temperamental crystallography still discouraged cutting of significant-sized rainbow calcites from the legendary St. Joe’s crystal until 1983.
The best of these stones would be cut by a former physical education teacher who had taken early retirement in 1980, and had turned to gem-cutting as a new vocation. Indeed, when Art Grant of Martville, N.Y., was entrusted with a 6,000-carat, heavily twinned calcite crystal from the Faraday Mine in Ontario, Canada, in 1982, he had cut only one other calcite, a 35-carat yellow stone from Russia. Excited by the challenge of a soft, cleavage-prone stone and guided mostly by intuition, Grant cut his first rainbow calcite, a 1,156-carat cushion now in the Harvard Mineralogical Museum. Gems and Gemology devoted a feature to this lapidary masterpiece in its winter 1984 issue. More masterpieces would follow.
Grant’s success with the Canadian calcite emboldened him to start cutting sections of a 75-pound chunk of the St. Joe crystal given him by museum curator George Robinson in 1982. From a lapidary standpoint, this chunk was the choice-est portion of the crystal. In October 1983, Grant cut a 915-carat cushion, now in the National Museum of Canada, then a 1,842-carat cushion and 1,077-carat rhomboid the next year. It wasn’t until late 1990 that he cut the next of his rainbow behemoths, a cushion weighing 836 carats. His last, and for many his greatest, work was an 1,830-carat kite shape cut less than a month later.
Perhaps the weightiest of all the St. Joe’s hunks left, this one too pounds, belongs to Dibble. But he won’t allow it to be cut. “It may be the best remaining record of the crystal,” he says, “and should be preserved as such.”
Please note: this profile was originally published in 1988 in Modern Jeweler’s ‘Gem Profiles: The First 60’, written by David Federman with photographs by Tino Hammid.
The rainbow calcite shown in the header is courtesy of Harold Dibble, Angola, N.Y. It was faceted by Art Grant.
