[Chemical composition] Al can be replaced by a small amount of Fe 2+ , Fe 3+ , Mg 2+ , and a small amount of Al-substituted Si. Sometimes it contains a small amount of K, Na, and Ca, and their position in the pyrophyllite is not clear, and may exist between the structural unit layers to compensate for the shortage of positive charges generated by Al-based Si. They also suggested that the surface adsorption of ions, or containing a small amount of inclusions caused by white mica.
[Crystal Structure] Pyrophyllite has two types: monoclinic and trigonal. Single oblique multi-type (2M) is more common; 
a 0 = 0.515 nm, b 0 =0.892 nm, c 0 = 1.895 nm; β = 99° 55'; Z = 2; slanting polytype (1Tc): Ci1-P1; a 0 = 0.517 nm, b 0 = 0.896 nm, c 0 = 0.936 nm; α = 91 ° 12', β = 100 ° 24', γ = 90 °; Z = 2. The TOT type, the octahedral sheet is composed of an [AlO 4 (OH) 2 ] octahedron and is a dioctahedral type.
[Form] Good crystal form is rare. It is often a leaf-like, scaly or cryptocrystalline dense block, sometimes a radial leaf-like aggregate (Figure G-44).
Figure G-44 Radiation leaf-like aggregate of pyrophyllite
[Physical properties] white, light green, light yellow or light gray; glass luster, dense block is oily luster, cleavage surface is pearl luster. The cleavage {001} is extremely complete; the cryptocrystalline dense block has a shell-like fracture. Hardness 1 to 1.5. The relative density is 2.65 to 2.90. It has a slippery feel and the cleavage sheet is flexible.
[Origin] and pyrophyllite occurrence extrusive rocks often acidic Al-rich, acidic or tuff by hydrothermal from junction metamorphic chips, but also in the epithermal gold-containing quartz veins. Our Fujian Shoushan, Qingtian pyrophyllite and other places, the Department of Cretaceous rhyolite and rhyolitic tuff formed by hydrothermal alteration.
[Identification characteristics] Similar to talc , the difference method is shown in the talc section.
[Main use] Basically the same as talc. In addition, pyrophyllite has a long history in the engraving process and seal making.
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