LARGE GREEN AGATE SLICE

THIS IS A LARGE NATURAL SLICE FROM BRAZIL READY FOR CABBING.

WEIGHT 294.65 CTS APP

SIZE 93 X 57 X 6 MM APP

Agate   is a microcrystallinE variety of quartz (silica), chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks but can be common in certain metamorphic rocks.

Colorful agates and other chalcedonieS were obtained over 3,000 years ago from the Achates River, now called Dirillo, in Sicily.

The first deposit on the wall of a cavity, forming the "skin" of the agate, is generally a dark greenish mineral substance, like celadonite  delessite or "green earth", which are rich in iron probably derived from the decomposition of the augite in the enclosing volcanic rock. This green silicate may give rise by alteration to a brown iron oxide (limonite), producing a rusty appearance on the outside of the agate-nodule. The outer surface of an agate, freed from its matrix, is often pitted and rough, apparently in consequence of the removal of the original coating. The first layer spread over the wall of the cavity has been called the "priming", and upon this base zeolitic minerals may be deposited.