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Geodes are hollow, vaguely spherical rocks, in which masses of mineral matter (which may include crystals) are secluded. The crystals are formed by the filling of vesicles in volcanic and subvolcanic rocks by minerals deposited from hydrothermal fluids ; or by the dissolution of syn-genetic concretions and partial filling by the same or other ...
Oregon Sunstone is unique in that crystals can be quite large. The copper leads to variant color within some stones, where turning one stone will result in manifold hues: the more copper within the stone, the darker the complexion. [9] On August 4, 1987, the Oregon State Legislature designated Oregon Sunstone as its state gemstone by joint ...
A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than 1 cm (0.4 in) and sometimes greater than 1 meter (3 ft). Most pegmatites are composed of quartz , feldspar , and mica , having a similar silicic composition to granite .
Botryoidal habit of gibbsite crystals. A botryoidal (/ ˌ b ɒ t r i ˈ ɔɪ d əl / BOT-ree-OY-dəl) texture or mineral habit, is one in which the mineral has an external form composed of many rounded segments, named for the Ancient Greek βότρυς (bótrus), meaning "a bunch of grapes". [1]
The crystal system of rhodochrosite is trigonal, with a structure and cleavage in the carbonate rhombohedral system. The carbonate ions ( CO 2− 3 ) are arranged in a triangular planar configuration, and the manganese ions (Mn 2+ ) are surrounded by six oxygen ions in an octahedral arrangement.
Jadeite is a pyroxene mineral with composition Na Al Si 2 O 6.It is hard (Mohs hardness of about 6.5 to 7.0), very tough, and dense, with a specific gravity of about 3.4.It is found in a wide range of colors, but is most often found in shades of green or white.
Material properties (size, color, texture) of fulgurites vary widely, depending on the size of the lightning bolt and the composition and moisture content of the surface struck by lightning. Most natural fulgurites fall on a spectrum from white to black. Iron is a common impurity that can result in a deep brownish-green coloration.
Porphyroblasts are commonly euhedral crystals, but can also be partly to completely irregular in shape. The most common porphyroblasts in metapelites (metamorphosed mudstones and siltstones ) are garnets and staurolites , which stand out in well- foliated metapelites (such as schists ) against the platy mica matrix.