• Chemistry: Al2Si2O5(OH)4, Aluminum Silicate Hydroxide • Class: Silicates • Subclass: phyllosilicates. • Groups: The Clays and the Kaolin Group. • Uses: In the production of ceramics, as a filler for paint, rubber and plastics and the largest use is in the paper industry to produce a glossy paper such as is used in most magazines. • Specimens Kaolin, which is named for its type locality, Kao-Ling, is a common phyllosilicate mineral. It lends it name to the Kaolin Group, members of which also belong to the larger general group known as the Clays. Kaolin's structure is composed of silicate sheets (Si2O5) bonded to aluminum oxide/hydroxide layers (Al2(OH)4) called gibbsite layers. ibbsite is an aluminum oxide mineral that has the same structure as these aluminum layers in Kaolin. The silicate and gibbsite layers are tightly bonded together with only weak bonding existing between these silicate/gibbsite paired layers (called s-g layers). The weak bonds between these s-g layers cause the cleavage and softness of this mineral. The structure is very similar to the Serpentine Group and at times the two groups are combined into a Kaolin-serpentine Group. Kaolin shares the same chemistry as the minerals halloysite, dickite and nacrite. The four minerals are polymorphs; meaning they have the same chemistry, but different structures. All four minerals form from the alteration (mostly weathering) of aluminum rich silicate minerals such as feldspars. Kaolin is by far the most common and most clay deposits contain at least some Kaolin. In fact, clay deposits will frequently be nearly 100% Kaolin pure! Kaolin is important to the production of ceramics and porcelain. It is also used as filler for paint, rubber and plastics since it is relatively inert and is long lasting. But the greatest demand for Kaolin is in the paper industry to produce a glossy paper such as is used in most magazines.
Kaolin - KSP1 Physical 100 <32 Particle Size Distribution [¥ì m] 100 <20 50 <2 10.5 At 105 ¢ªC Modulus of Rapture (kg/cm2) 18.8 At 900 ¢ªC 2.9 At 105 ¢ªC Shrinkage (%) 6.7 At 1250 ¢ªC 11.9 At 1400 ¢ªC 16.5 At 1250 ¢ªC Water Absorption (%) 10.9 At 1400 ¢ªC 93 Green Brightness (%) 97 At 1250 ¢ªC 98 At 1400 ¢ªC 2.31 Density Power (g/Cm3) 46 Plasticity ( Peff) H= 16 12500 Viscosity [CP] Sp: 3 R.P.M:5 Solid = 40% Water = 60% 7.3 Ph 48.10 SiO2 Chemical Analysis (%) 36.85 Al2O3 0.05 Fe2O3 0.52 TiO2 0.28 CaO - MgO 0.15 Na2O 0.36 K2O 13.69 L.O.I >91 Kaolin Mineralogical Composition (%) <2 Montmorilonit <3 Lllite - Calcite <5 Quartz - Feldspare
SiO2 68.050 Al2O3 22.298 TiO2 0.290 Fe2O3 0.160 CaO 0.140 MgO 0.275 K2O 0.173 Na2O 0.206 LOI 8.150
Hardness 1.5 - 2 (can leave marks on paper) Specific gravity 2.6 (average) Cleavage Perfect in one direction, basal Color Usually white, colorless, greenish or yellow Fracture Earthy Luster Earthy Streak White Transparency Crystals are translucent Crystal System Triclinic; 1 Crystal Habits Foliated and earthy masses. Crystals of any size are quite rare, usually microscopic. Other Characteristics Clay like properties when water is added. Best Field Indicators Habit, softness, color, luster and clay like properties
* Kaolin (a clay mineral) and mica can be substituted for talc in the production of rubber, paint, and plastics. * Kaolin can be used in place of talc in paper production. * Kaolin (a clay mineral) and mica can be substituted for talc in the production of rubber, paint, and plastics.