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Agate (/ ˈ æ ɡ ɪ t / AG-it) is a variety of chalcedony, [1] which comes in a wide variety of colors. Agates are primarily formed within volcanic and metamorphic rocks.The ornamental use of agate was common in ancient Greece, in assorted jewelry and in the seal stones of Greek warriors, [2] while bead necklaces with pierced and polished agate date back to the 3rd millennium BCE in the Indus ...
Hardstone carving, in art history and archaeology, is the artistic carving of semi-precious stones (and sometimes gemstones), such as jade, rock crystal (clear quartz), agate, onyx, jasper, serpentinite, or carnelian, and for objects made in this way. [1] [2] Normally the objects are small, and the category overlaps with both jewellery and ...
[4] [5] Most gemstones are hard, but some softer minerals such as brazilianite may be used in jewelry [6] because of their color or luster or other physical properties that have aesthetic value. However, generally speaking, soft minerals are not typically used as gemstones by virtue of their brittleness and lack of durability.
The agate has a hollow center, partially containing water. Enhydro agates can also contain debris or petroleum. Because the cavity is not full, the agate can produce sound from being shaken. Agates vary in size. The largest recorded agate was found in Fuxin City, China, with a diameter of 63 cm (24.8 in) and weighing 310 kg (683 lbs). [4]
The name moonstone derives from the stone's characteristic visual effect, called adularescence (or schiller), which produces a milky, bluish interior light. This effect is caused by light diffraction through alternating layers of orthoclase and albite within the stone.
Unpolished sunstone. The optical effect is due to reflections from inclusions of red copper, hematite, or goethite, in the form of minute scales, which are hexagonal, rhombic, or irregular in shape, and are disposed parallel to the principal cleavage-plane.
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Silica pseudomorph after gypsum crystals and silicified serpulid polychaete tubes Pseudomorph of goethite after pyrite. In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form (crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by another due to alteration, or ...