Monday, March 10, 2008

Greener than an emerald? no, but...prettier? oh yes - Dioptase

(Upper picture: Dioptase on dolomite crystals. Lower picture: Emerald).

It was just a matter of walking through some of the many displays in the 1979 Tucson Gem & Mineral Show, that I had already spent (mentally) around $2 million dollars in specimens, many of which simply took my breath away.

It was the first time I had the opportunity to attend this magnificent world class event, and my first time in the United States, what a great trip. Flew in an American Airlines Boeing 707 Mexico City-Tucson via Dallas, TX, my English was lousy, but I managed to get JIT (just in time) for the connection. Once in Tucson, Arizona, all was easier, nicer, got to the show so excited I wanted them all. But this time, though I dedicate the remembrance to the dioptase, (even its name is lovable). I met in Tucson with my college Mineralogy Professor Dr. Raul Ortiz Asiain and his daughters (Violeta, Magnolia, Dalia and China), all mineral experts, so we had a good time talking about minerals day and night for 3 days in a row eating McDonalds hamburguers on a non-stop basis either.

Didn't bring much money, about $300 dollars, even though it was sufficient to buy some, my budget was limited, because I still had to pay for hotels, meals (McDonalds), and transportation. One of the specimens I bought in the show ($10 US) was a superb nice combination of copper silicate (dioptase) on dolomite, both minerals of the same crystal system (Trigonal - Rhombohedral). The beauty of those cyclosilicate dioptase crystals is not easy to describe, other than its dark blue green, glassy in luster, transparent, well-formed coarse crystals features; I'd say this specimen is prettier than many emeralds I've seen, (which is too adventurous for some), but I admit my weakness for the dioptase, a mineral I thought it was an emerald, but ended up being originally from Tsumeb, Namibia, and not an emerald, but a dioptase. This is the story:

Late in the 18th century, copper miners in Kazakhstan thought they've found an emerald deposit. They found cavities in quartz veins in a limestone, filled with thousands of lustrous emerald-green transparent crystals. The crystals were sent to Moscow, Russia for analysis. However the mineral's inferior hardness of 5 compared with emerald's greater hardness of 8 easily distinguished it. Later, in 1797, René Just Haüy (famous French mineralogist) determined that the "emerald-like" Kazakhstani mineral was in fact not emerald, but a new mineral in science and named it dioptase (Greek, dia, "through" and optima, "vision"), as a consideration to the two cleavage directions of the dioptase, visible inside fine crystals.

Ok, this is the technical data of Dioptase:

Chemical Formula: CuSiO2(OH)2
Molecular Weight = 157.64 gm
Environment: Secondary mineral in oxidized zones of copper deposits.
Locality: Tsumeb and Cochab, Namibia; Altyn Tube, Russia.
Name Origin: From the Greek, dia - "through" and optomai - "vision."
Crystal System: Trigonal - Rhombohedral
Cleavage: [1011] Good
Color: Dark blue green, Emerald green, Turquoise.
Density: 3.28 - 3.35, Average = 3.31
Diaphaniety: Transparent to translucent
Fracture: Conchoidal - Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz).
Habit: Cryptocrystalline - Occurs as crystals too small to distinguish with the naked eye.
Habit: Crystalline - Coarse - Occurs as well-formed coarse sized crystals.
Habit: Massive - Uniformly indistinguishable crystals forming large masses.
Hardness: 5 - Apatite
Luminescence: None.
Luster: Vitreous (Glassy)
Magnetism: Nonmagnetic
Streak: Green

I wish you a terrific week, trouble free, and productive. In the mean time, till' my next posting, I hope you learned a bit more about the wonderful mineral world.

Best regards,

Oscar el Mexicano

PD: By the way, my return from that 1979 first visit to the Gem & Mineral Show in Tucson was via Aeromexico that used to stop in Hermosillo, Cd. Obregon, Culiacan, Guadalajara and finally Mexico City, an almost 8 hrs. trip!!!

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