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In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz. It is contrasted with mafic rocks, which are relatively richer in magnesium and iron. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Felsic magma or lava is higher in viscosity than mafic magma/lava.
The Mohs scale of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of minerals through the ability of harder material to scratch softer material.
Sandstone is a clastic sedimentary rock composed mainly of sand-sized silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Feldspar is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars. Feldspars make up about 60% of the Earth's crust, and 41% of the Earth's continental crust by weight.
Lustre is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back to the Latin lux, meaning "light", and generally implies radiance, gloss, or brilliance.
Trachyte is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava enriched with silica and alkali metals. It is the volcanic equivalent of syenite.
Amphibolite is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flaky) structure. The small flakes of black and white in the rock often give it a salt-and-pepper appearance.
Tanzanite is the blue and violet variety of the mineral zoisite, caused by small amounts of vanadium. Tanzanite belongs to the epidote mineral group. Tanzanite is only found in Simanjiro District of Manyara Region in Tanzania, in a very small mining area approximately 7 km (4.3 mi) long and 2 km (1.2 mi) wide near the Mererani Hills.
Nepheline, also called nephelite (from Ancient Greek νεφέλη (nephélē) 'cloud'), is a rock-forming mineral in the feldspathoid group – a silica-undersaturated aluminosilicate, Na3KAl4Si4O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites. It is used in glass and ceramic manufacturing and other industries, and has been investigated as an ore of aluminium.
Epidote is a calcium aluminium iron sorosilicate mineral.
Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. The classification of rocks is based on the information acquired during the petrographic analysis. Petrographic descriptions start with the field notes at the outcrop and include macroscopic description of hand-sized specimens. The most important petrographer's tool is the petrographic microscope. The detailed analysis of minerals by optical mineralogy in thin section and the micro-texture and structure are critical to understanding the origin of the rock.
Jadeite is a pyroxene mineral with composition NaAlSi2O6. 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. Jadeite is formed only in the subduction zones of continental margins, where rock undergoes metamorphism at high pressure but relatively low temperature.
Granulites are a class of high-grade metamorphic rocks of the granulite facies that have experienced high-temperature and moderate-pressure metamorphism. They are medium to coarse–grained and mainly composed of feldspars sometimes associated with quartz and anhydrous ferromagnesian minerals, with granoblastic texture and gneissose to massive structure. They are of particular interest to geologists because many granulites represent samples of the deep continental crust. Some granulites experienced decompression from deep in the Earth to shallower crustal levels at high temperature; others cooled while remaining at depth in the Earth.
Goldstone is a type of glittering glass made in a low-oxygen reducing atmosphere. The finished product can take a smooth polish and be carved into beads, figurines, or other artifacts suitable for semiprecious stone, and in fact goldstone is often mistaken for or misrepresented as a natural material.
The Spruce Pine Mining District is a swath of the valley of the North Toe River in the Blue Ridge Mountains of northwestern North Carolina. The area is mined for its mica, kaolin, quartz and feldspar. Spruce Pine district is one of the largest suppliers of high-purity quartz, which is used in the manufacture of silicon for integrated circuits. The district is named after the town of Spruce Pine, which is located in the middle of the region and is the hub of major mining activity there. The district is approximately 25 miles long and 5 miles wide.
Optical mineralogy is the study of minerals and rocks by measuring their optical properties. Most commonly, rock and mineral samples are prepared as thin sections or grain mounts for study in the laboratory with a petrographic microscope. Optical mineralogy is used to identify the mineralogical composition of geological materials in order to help reveal their origin and evolution.
Mount Du, which means Lonely Hill in Chinese, is a small mountain near Nanyang City, Henan province, China.
A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. pressure. Rocks which contain certain minerals can therefore be linked to certain tectonic settings, times and places in the geological history of the area. The boundaries between facies are wide because they are gradational and approximate. The area on the graph corresponding to rock formation at the lowest values of temperature and pressure is the range of formation of sedimentary rocks, as opposed to metamorphic rocks, in a process called diagenesis.
CheMin, short for Chemistry and Mineralogy, is an instrument located in the interior of the Curiosity rover that is exploring the surface of Gale crater on Mars. David Blake, from NASA Ames Research Center, is the Principal Investigator.
References
- ↑ "Saussuritization". global.britannica.com..
- Dietrich, R. V., 2005, Zoisite
- Insider Gemologist: What Are the Identifying Characteristics of These Green Gems?, July 15, 2005
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