Reference work entry
Agate is a cryptocrystalline silica colloidal aggregate. Its chemical composition is SiO 2. It can be monochromatic but more commonly has layers, stripes or bands of various colours. It is mainly found in cavities in extrusive volcanic rocks and is a low-temperature hydrothermal colloid mineral. It can also be found in sediments in residual slope layers or alluvial layers. The Chinese word for agate, ‘manao’, first appeared in Emperor Wei Wendi’s (220–225 A.D.) writing ‘Manao (agate) Lei Script’: ‘Agate is jade from the west with a staggered pattern like a horse brain and hence has the name manao’. Based on its colour and pattern, agate can be called hezi (black body with white or green dots in the middle) agate, jiezi (red and white band) agate, chanzi (twining) agate, blue agate, green agate, gao (plain white silk) agate, paste spot agate, moss agate, red agate and rhino agate (Fig. 8).
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