Spectacular Diaspore from Turkey
Steve Chamberlain
Fellow of the Academy
Even a confirmed
NYS collector occasionally gets excited about minerals from elsewhere. For me, some of the most interesting new
mineral specimens are the gemmy diaspore V-twins from near Pinarcik, Mugla,
Turkey. Dr. Murat Hatipoglu from Dokuz
Eylul University and I have written a detailed description for future
publication in Rocks and Minerals which I will summarize here.
Gem rough and faceted stones of diaspore with
outstanding color change (green in daylight and lavendar to peachy red in
incandescent light) began showing up on the internet several years ago. More recently, large V-twins have been
offered for sale. A very few fine
diaspore specimens, one of which I think may be the finest diaspore yet found,
turned up just last year.
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Figure 1. Map
showing the location of the gem diaspore locality southeast of Pinarcik, near
Mugla in southwestern Turkey. |
The
specimens are coming from a metamorphosed bauxite deposit in the Menderes
Massif in southwestern Turkey (fig. 1). Two
openings have been made on Little Pine Grove Hill (Kucuk Camlik Tepe) and
Big Pine Grove Hill (Buyuk Camlik Tepe). The metabauxite deposit was discovered in
1949 and first mined for aluminum ore in 1962. Initially, the government issued licenses
only for bauxite, so any gem diaspores had to be collected surreptitiously,
and some gem rough was exported between 1978 and 1982. In 2005, new mining
laws led to a private mining company, Zultanite Gems
Outstanding V-twins of translucent to transparent diaspore
occur singly and in clusters with calcite crystals, muscovite crystals,
chlorotoid crystals and earthy goethite in high temperature hydrothermal
veins. The veins fill nearly vertical fractures
in a zone along the contact between the metabauxite and enclosing marble. The mineralized zone appears to extend for at
least a mile. The accessory minerals
appear to form presentable mineral specimens, especially the chlorotoid
crystals, but virtually none are being collected and preserved. Most of the diaspore crystals are broken free
from the matrix and end up as crystal sections, singly-terminated crystals, or
occasionally V-twins with contact plane (061).
Only a few larger specimens have escaped this process, and they show
complex and very aesthetic three-dimensional arrangements of V-twins on matrix.
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Figure 2. Jeff Scovil’s photograph of the Gail Spann diaspore. The 9 cm by 5.6 cm specimen appears greenish-grey in daylight. |
Figure 3. Stuart Wilensky’s photograph of the Gail Spann diaspore in a different orientation. The specimen appears lavender in incandescent light. |
The discovery of two twin laws in diaspore post-dates Goldschmidt’s Atlas der Krystallformen and was made on microscopic diaspore crystals from metabauxites (diasporites) in France. To my knowledge, the Turkish V-twins are the first macroscopic twins ever found. One absolutely spectacular specimen was secured by Leonard Himes of Minerals America and sold to Texas collector, Gail Spann. Figures 2 and 3 show two photographs of the same specimen in two different lighting conditions and illustrate the color change.
Color change in diaspore seems to be caused by traces of chromium in the presence
of ferric iron. The iron largely causes
the olive-oil green color in daylight and the chromium causes the color change.
The daylight color is most often green, but can also be colorless,
light green, pale amber and brown. The incandescent-light color may range from
lavender to champagne to rose red and orange-red. Longer wavelength (lower wattage) incandescent
illumination often intensifies the color. Figure 4 shows a gem-quality cleavage of a Turkish
diaspore crystal photographed in daylight and incandescent illumination. The
color change is striking.
Collectors can only hope that the high prices garnered by diaspore specimens from this locality might drive their greater production. Look for these interesting specimens on the Internet and at mineral shows.
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Figure 4. Color change in Turkish diaspore. This gemmy, 4.5 cm cleavage fragment appears green in daylight (left), but rose red in incandescent light. Steve Chamberlain specimen and photos. |