Professional Jeweler Archive: Home on the Range

September 2003

Gemstones & Pearls/Gemology

Home on the Range

These agates contain portraits of make-believe landscapes. The only things missing are the deer and the antelope

Landscape agates are found on every continent. This one from southern Brazil originated as an agate geode and was cut into a thin slice, permitting translucency, which helps reveal nature’s handiwork. (A geode is a mineral and crystal-lined cavity that forms in cooling magmas near the earth’s surface.)

Landscape agates bring to mind the Wild West, with scenes of tree-studded mountains, rocky ravines and russet clouds and sunsets.

Agates – varieties of chalcedony – are composed of cryptocrystalline (microscopic), fibrous forms of quartz. They share many of quartz’s properties, except the way they look. How are they related if they look so different? Quartzes such as rock crystal, amethyst and citrine are in single-crystal form. Chalcedonies are composed of millions of tightly packed microscopic quartz crystals that still contain varying degrees of porosity. This porosity allows other minerals to leech into the pores, causing the spectacular variegated bands and peaks of color. Banded colors indicate areas more receptive to natural staining or dye.

The agate shown above has mainly reddish to yellow iron oxide stains. Very high power magnification may reveal the tightly bound structure of the minute crystals.

Agates were used as tools or decoration in prehistoric times and are even chronicled in The Bible. A description of several of the 12 stones that made up the High Priest Aaron’s Breast Plate in Exodus suggests many of the gems were agates. Agates were used also as trading beads throughout Africa, and a discovery of agate in mid-1300s near the Nahe River in Germany led to a major industry of gem cutting and bead-making in the twin towns of Idar and Oberstein.

When supplies of agate began to dwindle in Germany in the late 1800s, Brazil became the new source of material for Idar-Oberstein’s agate trade.

Landscape agates can be used in one-of-a-kind designer jewelry, though the gem pictured is more dazzling when observed under a combination of reflected and transmitted light. Because of its size (1-in.-by-4-in.), agates like this one can be used as “gee-whiz” displays in a stores or curio cabinets.

– by Robert Weldon, G.G.

Landscape agate from Rio Grande do Sul, Brazil, which was later cut and polished in Idar Oberstein, Germany. Photo by Robert Weldon.
Idar-Oberstein, Germany, one of the main cutting centers for gemstones, started out by cutting agates from the Nahe River region. This engraving, circa 1770, shows the cross-section of an agate polishing shop in Idar. Several cutters use a belly-down position while handholding the agates against the huge polishing laps.

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