Jewelry Lovers

Agate—diversely beautiful, multicolored, and variously formed as it is, its endless abundance of abstract designs can only be hinted at by the descriptions “spotted, cloudy, marbled, banded, or dappled.” To the ancient Greeks and Romans it was already known in the form of colored pebbles collected from the Achates River in Sicily.

Even the names for its fantastically imaginative pictures—the miniature paintings of tree, dendritic, landscape, moss, and lace agate—are only a modest selection from the inexhaustible wealth of attractive patterns. These dainty pictures, however, have no connection with fossilized plants or other organic residues, but consist of ramifying inclusions of true mineral substances which have crystallized out from ferruginous, manganese-rich, or chloric solutions. The ornamental stones are so-called cryptocrystalline mineral formations (the Greek word kryptos meaning “hidden” or “secret”), in whose dense aggregates the microscopically fine crystallites cannot be distinguished individually by the human eye.

The agate members of the chalcedony group, which in their turn belong to the quartz family, are descendants of volcanic eruptions, in whose hot molten lavas floated drops of more or less pure silica with or without water content, in sizes from that of a pea to some weighing a hundredweight. After the lavas solidified into melaphyre rocks the silica crystallized out as radial-fibered quartz masses of roughly almond-shaped form. The rate of crystallization of the silica was governed by the varying rate of cooling, which proceeded by irregular phases. In cyclical layers it precipitated either densely entwined, fine-fibered gray, or porous, coarse-fibered white bands. Such white- and gray-banded agates, whose merit lies in their pronounced capacity to absorb dyes, occur abundantly in the south Brazilian state of Rio Grande do Sul and in the district round Catalan in northern Uruguay.

The agates from the United States and from the melaphyre quarries near Idar-Oberstein (Germany) attract special notice by their pretty rose to red, and yellow to brown bands. By “pickling,” the porous white agate layers can be dyed. In this way the fine cryptopores between the quartz fibers are filled with, preferably, light-fast metallic coloring agents. By steeping in concentrated sugar solution or honey water, and subsequently treating with sulphuric acid, for example, black and white banded agate can be obtained. Drying and heating ensures the permanence of the colors in all agates dyed in this way: brown to red sand, reddish-brown carnelian, and the so-called layered seal stone or “niccolo.”

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