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Rutilated quartz is a variety of quartz which contains acicular (needle-like) inclusions of rutile. [1] It is used for gemstones. These inclusions mostly look golden, but they also can appear silver, copper red or black.
Rutile in quartz Within the igneous environment, rutile is a common accessory mineral in plutonic igneous rocks , though it is also found occasionally in extrusive igneous rocks , particularly those such as kimberlites and lamproites that have deep mantle sources.
The term "acicular" derives from the Late Latin "acicula" meaning "little needle". [1] Strictly speaking, the word refers to a growth habit that is slender and tapering to a point. Prismatic crystals are not acicular; however, colloquial usage has altered the commonly understood meaning of the word.
[1] [3] [4] Dumortierite is a fibrous variably colored aluminium boro - silicate mineral, Al 7 BO 3 (SiO 4 ) 3 O 3 . Dumortierite crystallizes in the orthorhombic system typically forming fibrous aggregates of slender prismatic crystals .
According to their experiment, at 1000 degrees with a pressure less than two kilobars the stable composition is a mixture of hedenbergite, olivine, and quartz. When the pressure moves to twenty kilobars, the composition moves towards the clinopyroxenes, which contains trace amounts of hedenbergite if any.
Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases, [1] [2] is an opaque, [3] impure variety of silica, usually red, yellow, brown or green in color; and rarely blue.
Quartz crystal with chlorite inclusions from Minas Gerais, Brazil (size: 4.2 × 3.9 × 3.3 cm) Chlorite is a common mineral, found in metamorphic, igneous, and sedimentary rocks. It is an important rock-forming mineral in low- to medium-grade metamorphic rock formed by metamorphism of mafic or pelitic rock. [ 9 ]
"Imperial Porphyry" from the Red Sea Mountains of Egypt A waterworn cobble of porphyry Rhyolite porphyry from Colorado; scale bar in lower left is 1 cm (0.39 in). Porphyry (/ ˈ p ɔːr f ə r i / POR-fə-ree) is any of various granites or igneous rocks with coarse-grained crystals such as feldspar or quartz dispersed in a fine-grained silicate-rich, generally aphanitic matrix or groundmass.