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Each month this section will feature either a topic of interest to gem lovers or one special gemstone with background on the material and its value.

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October, 1999

Dendritic, Moss and Plume Agates

A subvariety of chalcedony or microcrystalline quartz, these agates have in common that they contain mineral inclusions which may be any color, but share a roughly tree-like or branching form (dendron = tree). Those which have a more plant or feather-like appearance have been called moss or plume agates, respectively. All agates take a wonderful polish and are tough enough for most jewelry uses. Designers often take advantage of the intriguing patterns these stones have to offer.

Value

In general agate prices are quite modest with most of the price paying for the fashioning rather than the material itself. In the case of these agates, those with particularly distinctive or landscape like patterns or those of especially large size are at a premium. Custom cutting or pieces from collectible locations would be substantially more expensive. Pieces with especially fine patterns can be quite valuable.

Gemological Data:

Makeup: microcrystalline silicon dioxide

Luster: vitreous

Hardness: 7

Crystal structure: Trigonal

Fracture: conchoidal

Cleavage: none

Density: 2.61

RI: 1.53 - 1.54

Birefringence: 0.004

Pleiochroism: none

Dispersion: none

Stones Currently Available:

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