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Altering Quartz Minerals

A debate rages within the jewelry community, especially among those dealing with precious stones. Many precious stones are enhanced or altered. Green oil is forced into the cracks of emeralds. Nearly all blue topaz on the market began as a different shade. The premiere bead mineral, quartz, has been altered for millennia. So common are these alterations and so impossible is it to get the desired effect without altering, that it is widely agreed that a dealer need not disclose that these stones were altered.


One of the most common, and to most people surprising, alterations is done to makecarnelian. Look at the three stones above. The two on the left don't show the red color that characterizes carnelian, yet they will (or would if they were not in the Center's collection) become carnelians. On the far left is a stone I picked up at Ratanpur, the village where agate and carnelian are mined. In the center is a roughout from Cambay made from a similar stone. At right is a finished bead. It is red because it has been heated in a muffled furnace to bring out the red of the iron entrapped within the stone.

The ancient western Indian agate bead industry has been predominate for millennia because the stones were sitting in a layer of red silt and over the eons absorbed iron. The bead industry of Idar-Oberstein, Germany, relies on stones from Minas Gerais, Brazil, that have no natural iron in them, so they must be soaked in an acid bath with dissolved iron before being heated to turn red. A beadmaker at Pacitan, Indonesia insisted that his carnelians were naturally red. I told him that was unusual and told him about the Indian and German industries. As we left he whispered to the archaeologist who took me there that he did, indeed, have to heat his stones in a small furnace he built in the ground. I guess he figured the secret was out.

Onyxis a term derived from the Greek meaning "fingernail." It has been used to describe many stones. When used in the gem trade, it refers to a banded chalcedony with white and dark bands. It is almost always artificially made. At upper right is a piece of babaghoriaagate from the Medieval beadmaking center of Limudra, near Ratanpur. It has enough iron in it so that if heated the dark bands will turn red and formsardonyx. The Romans called this region theSardonyx Mountain.Some 4000 years ago Indians discovered that if the plain agate were soaked in sugar water or honey for a few weeks over a low heat and then heated, the dark bands would absorb the sugar and then caramelize, producing brown onyx (third from left). About 2000 years ago, apparently first at Arikameduin Southeast India, they put the soaked agate into sulfuric acid to carbonize the sugar making a black onyx (far right).

Do either of these stones exist in nature? Yes, sometimes, but there are very rare. At right is a piece of natural brown agate used as a blank to make stone blades. Nothing suggests that it was artificially colored. It is, however, a rare example. And where did I get it? From around the house I lived in for several years in Pune, India.


In addition to changing the color of stones, quartz stones have been altered in ways that decorate their surfaces.

The earliest of these decorations involves glazing the surface. Some soda and copper (for the color) was added to the surface and these would interact with the silicon dioxide of the stone, forming a thin layer of glass.

The bead shown here is from Iran and my best guess is that it dates to the 2nd to 6th centuries A.D. It has lost some of its glaze. Glazing stones goes back 6000 years in Egypt. In Early Islamic times (7th to 12th century A.D.) it was still being done in Iran.

Other examples of altering stone beads include their decorating. This group includes etched carnelian and dZi beads, visited here. Another famous altered quartz stone bead
is the Pumtek, made from opalized wood. Its story is

Thanks, Sindi


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