Quartz Quartz is hexagonal and commonly occurs as crystals ranging in size form microscopic to crystals weighing several tons. Where it crystallizes unhindered by other crystals, such as in cavities in rock or in a liquid containing few other crystals, it shows well-developed hexagonal prisms and sometimes showing apparent hexagonal pyramids or dipyramid. When it crystallizes in an environment where growth is inhibited by the surroundings, it rarely show crystal faces. It is also found as microcrystalline masses, such as in the rock chert, and as fibrous masses, such as in chalcedony. Vitreous lusture. As visible crystals, Quartz is one of the more common rock forming minerals. It occurs in siliceous igneous rocks such as volcanic rhyolite and plutonic granitic rocks. It is common in metamorphic rocks at all grades of metamorphism, and is the chief constituent of sand. Because it is highly resistant to chemical weathering, it is found in a wide variety of sedimentary r
STRUCTURES OF METAMORPHIC ROCKS (MACROTEXTURES): (i) Slaty cleavage : A pervasive, parallel foliation (layering) of fine-grained platy minerals (chlorite) in a direction perpendicular to the direction of maximum stress. It produces the rocks slate and phyllite. (ii) Schistose : Schist has a lepidoblastic foliation if this foliation is defined by oriented mica, and a nematoblastic foliation if such a foliation is defined by the orientation of prismatic minerals as amphiboles and pyroxenes. (iii) Gneissic : A complex banded texture made of schistose layers or bands alternating with bands commonly characterized by a granoblastic texture. (iv) Granoblastic: Granular, interlocking equi-dimensional grains of subequal size; no preferred orientation or cleavage. (v) Hornfelsic : Fine-grained, granular interlocking grains, possibly of variable shapes and sizes. No preferred orientation. (vi) Cataclastic : •
I would like to read something on igneous rock. Please if you have any information can you please share it with me.
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