About the History and Properties of Kunzite Gems

Kunzite is a comparatively new transparent gem discovered in America about 1903; it is a lilac-coloured spodumene, which, upon the suggestion of the mineralogist Charles Baskerville, was named kunzite, in honour of Dr. George Frederic Kunz, because of his services to the scientific world in the gem branch of mineralogy. The honour accorded Dr. Kunz by mineralogists in accepting the name is enhanced because of the beauty of this new gem mineral. The first crystals of this unaltered lilac-coloured spodumene were discovered a mile and a half north-east from Pala, San Diego County, California. The vicinity of this discovery was already of great interest to students of gem minerals because but fifty feet away from the spot is a famous deposit of tourmaline from which specimen crystals remarkable for the unusually large size and great beauty have been taken, while half a mile away is a celebrated rubellite and lepidolite locality. The spodumene crystals found near Pala are of extraordinary size, one weighing thirty-one ounces, troy; the dimensions of this crystal were 18 x 8 x 3 centimetres.

Kunzite has a considerable range of tints which include shades characterised as: deep rosy lilac, rich deep pink purple, and delicate pink amethystine; this and the lighter lilac shades are the typical tints. The finest specimens we have seen have a bright lustre and perfect transparency. These lilac-spodumene crystals occurred in a ledge which was traced for twelve hundred feet along the top of a ridge. The rock is a coarse decomposed granite, which might be termed pegmatite, with the feldspar much kaolinised and reduced to a "red dirt," and showing many large quartz crystals, some of them weighing 150 pounds, but not clear.

Other coloured crystals of spodumene which approach in colour and quality the standard specimens obtained near Pala have been found at Meridian, California, but these are smaller than those found at Pala; the Meridian specimens more nearly resemble the occasional specimens of unaltered spodumene found near Branchville, Connecticut. The Meridian crystals were at first supposed to be tourmaline, but were identified by Dr. Kunz; many of these crystals were ruined by lapidaries who unsuccessfully tried to cut them, as the very highly facile cleavage of spodumene caused the mineral to flake.

Kunzite is entirely distinct from the green variety of spodumene (hiddenite), the beautiful gem mineral found at Stony Point, Alexandra County, North Carolina, and from the transparent yellow variety reported by a mineralogist named Pisani to have been found in Brazil, and, since its discovery, produced in sufficient quantity to come into use as gems.

Spodumene--it is also sometimes called triphane--in its general characteristics is a member of the pyroxene group, and is the only gem mineral, besides lepidolite and tourmaline, which contains a considerable proportion of lithium. The chemical composition of spodumene is: silica, 64.5; alumina, 27.4; and lithia, 8.4. Spodumene is fusible before the blowpipe; its hardness is 6 1/2 to 7; specific gravity, 3.1-3.2; lustre, vitreous. Spodumene is commonly white or grey, and because of that it was named, the word spodumene being derived from the Greek spodios, meaning ash-coloured. Most of the spodumene found is opaque, only the gem quality being translucent to transparent. Spodumene crystallises in the monoclinic system, and crystals have been found four feet long.

Until the discovery of kunzite the use of spodumene as a gem was limited to the emerald-green hiddenite, named after its discoverer, W. E. Hidden. This variety occurs in thin crystals with tints ranging from colourless to yellow and to an emerald green. Five carats is about the maximum weight of cut hiddenite gems; they are cut into step or table stones to make the most of their dichroism, and to avoid the possibility of splitting because of their unusually high degree of prismatic cleavage.

The Brazilian spodumene, the yellow, was originally identified as chrysoberyl, and it is used in jewelry as the last named metal is; scientific tests will easily distinguish these two minerals the one from the other. Some spodumene of a beautiful blue colour has also been found in Brazil, near Diamantina.

Kunzite, almost 7 in hardness, is transparent and pleochroic. Viewed transversely some representative crystals were faintly pink; longitudinally they presented a rich pale lavender colour, approaching amethystine. A characteristic of kunzite crystals is a peculiar etching, apparently effected with solvents. A number of scientific tests have revealed in kunzite a remarkable phosphorescence, not possessed by other varieties of spodumene similarly tested, and its illuminant powers, excited by its bombardment with Rontgen rays, and also by the proximity of a few milligrammes of radium bromide, mark this mineral as unique and of unusual interest to scientists, in addition to its value as a recruit to the first rank of semiprecious stones.

In a description of experiments made upon kunzite Sir William Crookes writes:

But the most interesting thing to me is the effect of radium on it. A few milligrammes of radium bromide brought near the piece of kunzite makes it glow with a fine yellowish light, which does not cease immediately on removal of the radium, but persists for several seconds.

I have found some diamonds phosphoresce brightly under the influence of radium, and have been searching for a mineral which is equally sensitive. I think this lilac variety of spodumene runs the diamond very close, if it does not surpass it sometimes.

The luminosity of kunzite, in response to the artificial conditions already known to arouse it, is thus summed up, in a sentence, by Dr. Kunz:

In a word, kunzite responds to radium, actinium, Rontgen and ultra-violet rays; it is thermoluminescent and pyro-electric. Becomes radescent when mixed in powdered form with radium; becomes incandescent when this mixture is slightly heated, and crystals or gems become beautifully phosphorescent for quite a time by passing a faradic current through it, or if held between the poles of a Holtz machine.