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Oxide Analysis Formula
Li2O 4.87% 1.00
Al2O3 16.65% 1.00
SiO2 78.49% 8.00
Oxide Weight 612.54
Formula Weight 612.54


Petalite is a lithium aluminum silicate mineral (more simply a lithium feldspar) that is commonly used in clay bodies. It is valuable because it provides an insoluble source of lithium and has the highest Li2O:Al2O3 ratio of any natural mineral. Lithium is a strong alkaline flux and is effective over all temperature ranges. It imparts lower expansion and gives unique color response to copper and cobalt in glazes. Some commercial versions have a chemistry that fairly closely matches the theoretical chemistry given here.

Petalite is most prized for its mineralogical properties. It is especially valuable in imparting thermal shock resistance to clay bodies because it has almost zero expansion when heated above 700C. Bodies with 60%+ petalite can take a direct flame and rapid water cooling without failure. To make a plastic clay body mix petalite with as much ball clay as needed. For a casting body, use as much kaolin as needed to achieve the desired casting properties. Bentonite can be added to either type of body to increase the petalite proportion.

One serious problem with low expansion petalite bodies is that it is very difficult to achieve glaze fit. All common glazes will craze. This is compounded at lower temperatures where the limited low-expansion silica and alumina necessary for melting raises glaze expansion. For some low-expansion bodies, it is almost impossible to match a glaze

Petalite can be used to create low expansion glazes. It is suitable for white and transparents as well because of the low iron content. It does not present the frothing problems sometimes associated with spodumene and helps improve brightness. One formula suggested by Val Cushing is petalite 76.9, talc 14.2, whiting 3.4, kaolin 5.5. This glaze is claimed to have an expansion of 0.8 x 10 -6 and fires cone 9 to 12 with a silky surface.

Spodumene and lepidolite also provide insoluble sources of lithium. However, spodumene is more refractory, thus producing more porous fired results. If a body's range needs to be extended, spodumene can thus be added in preference to silica. Petalite is slightly more refractory than lepidolite.

P.C.E.: 15
P.C.E. 45% petalite:55% F4 Feldspar: 4
P.C.E. 45% petalite:55% Nepheline Syenite: 2

A petalite clay body can be made by combining petalite and ball clay or kaolin in proportions that provide a good compromise between high petalite content and necessary plasticity.

Petalite promotes the conversion of the quartz form of silica to the cristobalite form. This has implications on the thermal expansion of the fired matrix.

Related Information


Petalite at Wikipedia
Typecodes Materials used in Denmark
Typecodes Generic Material
Generic materials are those with no brand name. Normally they are theoretical, the chemistry portrays what a specimen would be if it had no contamination. Generic materials are helpful in educational situations where students need to study material theory (later they graduate to dealing with real world materials). They are also helpful where the chemistry of an actual material is not known. Often the accuracy of calculations is sufficient using generic materials.
Typecodes Feldspar
The most common source of fluxes for high and medium temperature glazes and bodies.
Glossary Cristobalite Inversion
In ceramics, cristobalite is a form (polymorph) of silica. During firing quartz particles in porcelain can convert to cristobalite. This has implications on the thermal expansion of the fired matrix.
Materials Spodumene
Materials Amblygonite
Materials Lepidolite
Materials Triphylite
Hazards Fluorine Gas
Can you be exposed to fluorine gas in ceramics. Yes, if you are using materials that contain fluorine. These are not many, but worth knowing about.
Oxides Li2O - Lithium Oxide, Lithia


Co-efficient of Linear Expansion0.15
Frit Softening Point1350C M
Density (Specific Gravity)2.45

By Tony Hansen

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