Red Tourmaline - more pics

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DFW PS GTG Planner Extraordinaire :)

Skippy

"The only things that stand between a person and what they want in life are the will to try it, and the faith to believe it's possible" Rich Devos

A Girl's Best Friend

Chrono, you really hit on something that has been nagging at me for some time! I studied geology in college.  (I don't mean that I majored in it!  I mean that I took one course in it as well as a course or two in physical geography!)  I have forgotten most of what I knew about rock crystals and I never knew much...although I recall looking at a large rock that  I was told was a garnet and having to learn about its structure!!!  (I would remember the garnet, not the granite, wouldn't I!!??)

At any rate, I didn't know what rubellite was!  I heard the word, but I had no idea it was just pink tourmaline.  I think I vaguely asociated it with rhodolite garnets in my mind!

At any rate, I looked up toumalines and was astounded to see that not only are rubellites tourmalines, but so are peridots!  Thank you for the heads up!  I had better spend more time in Colored Stones!  I am always in the The Gold Thread!!!

This quotation is from Old and Sold Antiques Digest.

"TOURMALINE is unsurpassed even by corundum in variety of hue, and it has during recent years rapidly advanced in public favour, mainly owing to the prodigal profusion in which nature has formed it in that favoured State, California, the garden of the west. Its comparative softness militates against its use in rings, but its gorgeous coloration renders it admirably fitted for service in any article of jewellery, such as a brooch or a pendant, in which a large central stone is required. Like all coloured stones it is generally brilliant-cut in front and step-cut at the back, but occasionally it is sufficiently fibrous in structure to display, when cut en cabochon, pronounced chatoyancy.

The composition of this complex species has long been a vexed question among mineralogists, but considerable light was recently thrown on the subject by Schaller, who showed that all varieties of tourmaline may be referred to a formula of the type 2S 1 02. 3 B203.(9 —x)[(A1,Fe)203].3x[(Fe,Mn,Ca, Mg,K2,Na2,Li2,H2)O].3H20. The ratios of boric oxide, silica, and water are nearly constant in all analyses, but great variation is possible in the proportions of the other constituents. Having regard to this complexity, it is not surprising to find that the range in colour is so great. Colourless stones, to which the name achroite is sometimes given, were at one time exceedingly rare, but they are now found in greater number in California. Stones which are most suited to jewellery purposes are comparatively free from iron, and apparently owe their wonderful tints to the alkaline earths ; lithia, for instance, is responsible for the beautiful tint of the highly prized rubellite, and magnesia, no doubt, for the colour of the brown stones of various tints. Tourmaline rich in iron is black and almost opaque. It is a striking peculiarity of the species that the crystals are rarely uniform in colour throughout, the boundaries between the differently coloured portions being sharp and abrupt, and the tints remarkably in contrast. Sometimes the sections are separated by planes at right angles to the length of the crystal, and sometimes they are zonal, bounded by cylindrical surfaces running parallel to the same length. In the latter case a section perpendicular to the length shows zones of at least three contrasting tints. In the Brazilian stones the core is generally red, bounded by white, with green on the exterior, while the reverse is the case in the Californian stones, the core being green or yellow, bounded by white, with red on the exterior. Tourmaline may, indeed, be found of almost every imaginable tint, except, perhaps, the emerald green and the royal sapphire-blue. The principal varieties are rose-red and pink (rubellite) (Plate XXVII, Fig. I), green (Brazilian emerald), indigo-blue (indicolite), blue (Brazilian sapphire), yellowish green (Brazilian peridot) (Plate XXVII)"

AGBF

A Girl's Best Friend

_______________________________ "Women are either goddesses or doormats." Pablo Picasso "In all matters of opinion, our adversaries are insane." Mark Twain

You are quite right, klewis.  I am guilty of sloppy reading!  It did not say that in the article I quoted  that a peridot was another term for a variety of tourmaline but only that the terms, "Brazilian peridot" and "Ceylonese peridot" were terms used for varieties of tourmaline.  Peridot has an entirely different composition.  I went and looked it up (here)!

"Peridot (pronounced pair-a-doe) is the gem variety of olivine. Olivine, which is actually not an official mineral, is composed of two minerals: fayalite and forsterite. Fayalite is the iron rich member with a pure formula of Fe2SiO4. Forsterite is the magnesium rich member with a pure formula of Mg2SiO4. Olivine's formula is written as (Mg, Fe)2SiO4 to show the substitution of the magnesium and iron. Peridot is usually closer to forsterite than fayalite in composition although iron is the coloring agent for peridot. The best colored peridot has an iron percentage of less than 15% and includes nickel and chromium as trace elements that may also contribute to the best peridot color.
 
Gem quality peridot comes from the ancient source of Zagbargad (Zebirget) Island in the Red Sea off the coast of Egypt; Mogok, Myanmar (formerly known as Burma); Kohistan, Pakistan; Minas Gerais, Brazil; Eifel, Germany; Chihuahua, Mexico; Ethiopia; Australia; Peridot Mesa, San Carlos Apache Reservation, Gila County, Arizona and Salt Lake Crater, Oahu, Hawaii, USA. The best quality peridot has historically come either from Myanmar or Egypt. But new sources in Pakistan are challenging that claim with some exceptional specimens. The Arizona gem material is of lesser quality, but is far more abundant and is therefore much more affordable. An estimated 80 - 95% of all world production of peridot comes from Arizona. The Myanmar, Pakistani and Egyptian gems are rarer and of better quality and thus quite valuable approaching the per carat values of top gemstones. Possibly the most unusual peridot is that which comes from iron-nickel meteorites called pallasites. Some are actually facetted and set in jewelry."

AGBF

A Girl's Best Friend

mr. ma re