Geode

D-23-GEODEITS–A geode is a hollow, more or less globular body, up to 30 cm or more in diameter, found in certain limestone and volcanic rocks, and very rarely in shale.

Significantfeatures include athin outer layerof dense Chalcedony, partial filling by inward projecting crystals, generally quartz or calcite but sometimes barite or celestite, and shows of evidence of growth through its expansion.

Unlike a druse, a geode is separable from the rock in which it occurs and its crystals are not of the same minerals as those of the enclosing rock.

(Chalcedony is a cryptocrystalline variety of quartz. It is commonly microscopically fibrous, may be translucent or semi transparent, and has a nearly wax like luster. Chalcedony often occurs as a deposit filling or lining cavities in rocks).

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