The pegmatites, those of Nilaw and Mawi especially, occur as veins of highly variable size, from 10 cm to 40 meters in thickness and from a few meters to a few kilometers in length, in what has been called the plutonic intrusion of Nilaw (Fuchs et al.
Pegmatites are recognizable in the local topography as small hills, due to the relative hardness and resistance to weathering of the pegmatites in relation to the country rock.
Pegmatite
Pegmatites are one of the more significant varieties of intrusive, mafic igneous rock, due to their higher concentration of rare-earth minerals and gemstones.
Pegmatite -
Natural igneous rock formation usually characterized by a coarse texture caused by crystallization from an exceptionally fluid magma rich in mineralizers containing rare elements
Rarity factors - ...
Pegmatites
When magma in the upper part of the mantle becomes concentrated with volatiles it cools into a cavity called a pegmatite.
Pegmatites
A pegmatite is a body of plutonic rock which contains unusually large crystals. Crystals measuring thirty centimeters across are common.
Pegmatites: As magma, which contains dissolved minerals in water under pressure, begins to rise through cracks and cool down, crystallization begins.
Pegmatite - A light coloured igneous rock containing large crystals of the minerals mica, quartz and feldspar.
Pegmatite
A coarse, intrusive igneous rock featuring extremely large crystals (some over 50mm in size).
pegmatites, high temperature to low temperature hydrothermal veins, replacements in chalks
Association:
sphalerite, chalcopyrite, pyrite, barite, fluorite,calcite ...
Pegmatite may be produced by low degrees of partial melting of the crust.
Pegmatites.....A very coarse platonic rock, generally granitic in composition. Usually forming dikes that cut granite or the gneisses and schists that border granite masses.
The region of pegmatite dikes in the state of Minas Gerais in Brazil has been the primary source of gem beryl and several other species of colored gemstones for many years.
Bastin's "Pegmatites in Maine".A complete book on Maine's Tourmalines !!
George Frederick Kunz on Maine Tourmaline
Kunz report in USGS 1908 on "Maine Tourmaline" ...
Exclusively in pegmatites, or as water worn, frosted pebbles or cobbles in stream gravels. Single crystals weighing up to 243 pounds are known.
pegmatite A coarse-grained igneous rock with exceptionally large crystals, formed from a magma that contains a high proportion of water. pendant Ornament or piece of jewelry that hangs down, such as from a necklace or earrings.
Bastin (1911), Geology of the Pegmatites and Associated Rocks of Maine
Bates (1895), Quartz and its varieties
Bauer & Spencer (1904), Precious stones, a popular account of their characters, occurrence and applications ...
Pegmatite - A coarsely crystalline area in an igneous formation. Many gem minerals form in pegmatites.
Penetration Twin - A twinned crystal where one crystal has intergrown with another. (Fluorite, Pyrite) ...
Most topaz is formed in pegmatite rock deposits, which when weathered release topaz and other gems into alluvial deposits. Brazil is the largest producer of fine gem quality Topaz, specifically in the state of Minas Gerias.
Occurrence - This stunning pink colored gemstone occurs in complex granite pegmatites in squat, tabular crystal form. It is also found alluvial deposits owing to its high specific gravity and hardness.
The pegmatite dikes of Haddam Neck, Conn., of Stoneham, Me., and of San Diego County, Cal., have furnished splendid aquamarine and other beryl.
In addition to basic and silicic igneous rocks, a third igneous mineral environment representing the final stages of igneous fractionation is called a pegmatite (PEG) which is typically very coarse-grained and simi lar in composition to silicic ...
The Lily Pond mine in a pegmatite near a small lake was the source of crystals accompanied by other pale greenish-blue, bluish-green, yellowish, pink, and white Beryl crystals. Dr.
It is found as a constituent rock-forming component in feldspar rich granitic and syenitic pegmatites.
Gemstone Physical Characteristics: Sunstone can contain tiny flecks or inclusions called snowflakes, consisting of copper or hematite.
Sapphires are formed in a syenite and pegmatite secondary deposits such as inthe alluvial deposits from the weathering of the parent rocks which is called byon. Sapphire grows in the form of a hexagonal bi-pyramid of twelve triangular faces.
Topaz is one of the well-known pegmatite minerals that also includes beryl and tourmaline. Blue topaz has a definite, uniform color ranging from sky blue to Swiss blue.
Golden beryl was discovered in Namibia in 1913 in a pegmatite that also produced aquamarine.
The minerals of the Cairngorms are generally associated with granitic pegmatites. Beryl crystals (see photos above & below), topaz, microcline and quartz fragments, the traditional minerals of the mountains, are still occasionally found.
Occurrence
Often found in pegmatites, black tourmaline is rich in iron, and very common. Tourmaline and opal are the birthstones of the month of October. Tourmaline is the national gemstone of the United States.
Comments:
Forms most commonly in pegmatites.
Inaccurate data? Better photos? .
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" It was discovered in Namibia in the year 1910 in a pegmatite. Today, the deposits of heliodor are found in Minas Gerais and Goias in Brazil, the Ukraine in Russia, and Connecticut and Maine.
Crystallized pure silica occur in pegmatite. Available in many colors most common. White, pink (Rose quartz), yellow (Citrine) and purple (Amethyst).
Hardness : 7 Refractive Index : 1.554-1.553 Density : 2.66 ...
Minerals formed during injection of deep hot fluids and pegmatite formation.
Metamorphic Minerals
Minerals forming in solid rocks under prolonged heat and pressure.
Pegmatites in the State have produced colorless and pale yellow herderite crystals from which small gems have been cut. Oxford County deposits have produced colorless, facet-grade phenakite from which small to medium stones have been cut.
Apatite
Apatite is an abundant mineral found in many types of rock but most gem quality material is associated with pegmatites.
Applique
An ornamental object which was produced separately and then applied to a piece of jewelry.
The most popular of the other beryls is probably Morganite, which is pastel pink to peach or lavender. It was first discovered in California in the Pala pegmatites in 1905, and later in Madagascar.
Tourmalines are found in pegmatite veins in granites, gneisses, schists, and crystalline limestone. Important sources include Elba, Brazil, Russia, Sri Lanka, and parts of the U.S. Tourmaline scores a 7.0 on the Mohs scale.
Morganite is typically associated with quartz, albite and muscovite, and can occur with other pegmatite accessory minerals such as garnet, spodumene, columbite-tantalite, lepidolite, amblygonite, tourmaline, petalite, ...
The occurrence of Thomsonite is shared with other zeolites in the amygdaloidal craters of basaltic volcanic rocks and in rare instances the stone exists in granitic pegmatites.
The world has one man and his unshakable belief to thank for the discovery of this unique gemstone: Heitor Dimas Barbosa. Tirelessly, he and his assistants spent years digging in the pegmatite galleries of some modest hills in the Federal Brazilian ...
 See also: Crystal, Stone, Mineral, Color, Gemstone
  
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