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talc

talc
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Product Description

General
Category Silicate mineral
Chemical formula
Mg3Si4O10(OH)2

Crystal symmetry
Either monoclinic or triclinic

Identification
Color Light to dark green, brown, white
Crystal habit
Foliated to fibrous masses, rare as platey to pyramidal crystals
Crystal system
monoclinic or triclinic

Cleavage
Perfect on {001} basal cleavage

Fracture
Flat surfaces (not cleavage), fracture in an uneven pattern

Mohs scale hardness 1 (defining mineral)
Luster
Waxlike or pearly
Streak
White to pearl green
Diaphaneity
Translucent
Specific gravity
2.58 to 2.83



Pleochroism
Weak in dark varieties
Ultraviolet fluorescence
Short UV=orange yellow, long UV=yellow

Analysis
No. 1 of talc
SiO2 MgO Fe2O3 Al2O3 L.O.I Bright
62.16 31.54 0.15 0.32 4.68 96
Grade No. 2
SiO2 MgO Fe2O3 Al2O3 L.O.I Bright
62.7 30.94 0.19 0.36 4.81 85


Grade No. 3
SiO2 MgO Fe2O3 Al2O3 L.O.I Bright
62.51 30.34 0.31 0.38 5.02 77






general

Talc is a metamorphic mineral resulting from the metamorphism of magnesian minerals such as serpentine, pyroxene, amphibole, olivine, in the presence of carbon dioxide and water. This is known as talc carbonation or steatization and produces a suite of rocks known as talc carbonates.
Talc is primarily formed via hydration and carbonation via the following reaction;
serpentine + carbon dioxide ? talc + magnesite + water
2 Mg3Si2O5(OH)4 + 3CO2 ? Mg3Si4O10(OH)2 + 3 MgCO3 + 3 H2O
Talc can also be formed via a reaction between dolomite and silica, which is typical of skarnification of dolomites via silica-flooding in contact metamorphic aureoles;
dolomite + silica + water ? talc + calcite + carbon dioxide
3 CaMg(CO3)2 + 4 SiO2 + H2O ? Mg3Si4O10(OH)2 + 3 CaCO3 + 3 CO2
Talc can also be formed from magnesian chlorite and quartz in blueschist and eclogite metamorphism via the following metamorphic reaction:
chlorite + quartz ? kyanite + talc + water


Talc is an important industrial mineral. Most commonly it is known as the primary ingredient in talcum powder. Its resistance to heat, electricity and acids make it an ideal surface for lab counter tops and electrical switchboards

Available in nature as sheeted bulk , veins , lenses or with basic ultra basic metamorphic rocks of serpentinete schist and gneiss ,it may contain related sheet silicates such as chlorite and serpentine, plus prismatic tremolite, anthophyllite, and carbonates such as magnesite, dolomite, and calcite .
-Talc have several kinds
1- steatite which is pure talc, it refers to high-purity, dense, very fine-grained talc that can be machined. On firing, it has good electrical insulating properties and is used in the manufacture of electrical porcelain.
2-foliated talc use in several industry
3- tremolite talc This is fine-grained “hard” talc , which have magnesium concentration about 10 % , and traces of carbonates and quartz. .
Uses :
Talc enter in several industry around the world like
1- painting 2- insecticides : as a carrier
3- tanning leather 4- soap
5- filler : in carpet and textile backings, wallboard joint compounds, adhesives and sealants
6- ceramic and pottery : Talc for ceramic applications is low in iron and carbonates, uniform in chemical composition and fired shrinkage, hard and fine grained, controlled in particle size distribution, and white or near-white firing In low-fire artware bodies it imparts whiteness and increases thermal expansion to resist crazing. In stonewares, small percentages of talc are used to flux the body and therefore improve strength and vitrification. It is a source of MgO flux in high temperature glazes (to control melting temperature). It is also employed as a matting agent in earthenware glazes and can be used to produce magnesia mattes at high temperatures. Talc’s high fusion point and fluxing action enable lower firing temperatures and quicker firing schedules to be used in the production of wall tiles, sanitaryware, vitreous china
7- plastics : Talc is used in thermoplastics to control melt flow, reduce creep in molded parts, increase molding cycles, increase heat deflection temperature, and improve dimensional stability , largest use is in polypropylene to increase both stiffness and resistance to high temperature creep. The main requirements for plastics-grade talc are low iron, low moisture, and low abrasion. The color required depends on the finished plastic.
8- paper : Its low abrasion and ability to preferentially wet oily materials in the presence of water are unique among mineral alternatives , talc is used for TiO2 extension and for improved gloss, opacity, brightness, and ink holdout.
9- pharmacological cosmetics and talc powder : Only high-brightness platy talc of exceptional purity is used in cosmetics and pharmaceuticals. The ta