Lee Horowitz, the July guest speaker at D.C.GIA, wears many hats; foremost among them is the passionate lover of Peruvian opals. He is an owner, miner, cutter, producer, promoter and dealer of Peruvian opals and other South American minerals.
Mr. Horowitz stood alongside a table loaded with specimens of his gems both rough and finished in pieces of jewelry.
They were spectacular!
BLUE AND PINK PERUVIAN OPALS
Peruvian blue opal is classified as a common opal, a silicate containing water that has no play of color and is distantly related to quartz. Common opal is found in other localities as well; Oregon, Mexico, Kenya, Tanzania, etc. But it is the Peruvian blue opal that stands out. The blue has a hardness of 5.5( under the 7.0 of quartz ) and is colored by copper.
The Andean blue opal became an immediate hit at the Tucson show of 1998-1999 and much of the rough was bought by India and China. As a result the top quality is scarce and expensive.
Mining is touchy; the major problem is water. Evaporation of the internal water causes loss and change of color and cracking.
The Peruvian blue comes in many shades and the best blue with the least mineral inclusions is termed super. Premium blue is considered superior or second in color and the rest is termed mine run or junk. India and China buy mine run and dye this discolored material. The dye can be detected by testing with acetone.
There are a number of simulants on the market; glass, Victoria stone, dyed chalcedony and others. These have either a different hardness or specific gravity or refractive index.
The pink Peruvian opal is a strawberry pink; the deeper the color the more desirable and expensive the specimen. It has a hardness of 5.5 . It is graded like the blue opal from the rare pink/red, druzy with mineral crystal toppings, to the deeper pink, super pink and mine run that is a washed-out color with much gray. The opals can have dendritic inclusions of manganese and/or iron. Petagorskite enables the pink to take a good polish. As with the blue opal, the pink also has water problems and the dehydration can cause color changes.
OTHER ANDEAN AND SOUTH AMERICAN MINERALS
Rhodonite and rhodochrosite, colored red or pink by manganese, are found in Argentina, Brazil and Peru. The exceptionally popular Ortiz rhodochrosite is a red with plum overtones unlike the brown from Africa or the deep pink of Alma Colorado. The Andean sources are on the verge of becoming depleted as is the stalactite source from there. The bacon white striped specimens are unusual and much in demand.
Pink rhodonite is a lovely pink opaque material.
Amazonite, with a hardness of 5-6, is a natural turquoise blue from the Amazon basin and a green from the Andes Mountains.
Angellite is found as gray nodules and is a blue colored anhydrite of alabaster.
Sodalite comes from Bolivia and is a deep blue like the Chilean lapis.
Copper-based chrysocholla, related to turquoise, is found in massive form with a hardness of 4.5. Again this material is graded like the opals as super, secondary and mine run. The Peruvian mine is closed but chrysocolla is found in Mexico, Brazil, Zambia and Arizona. It is sold in Israel as the Elat stone, cheaper than turquoise and stabilized.
Other minerals found are: gem silica which is translucent to opaque colored by chrysocholla, opalite, fluorite, patterned lepidolite, demerterite, serpentine, onyx and many etceteras.
The speaker, the speech, the information and the specimens were a resounding success. Many thanks Mr. Horowitz.
Meeting Summary written by Ms. Lisa Carp
Photos by Mrs. Melanie Marts