Petalite

Chemistry

K2O	0.260
Li2O	4.320
Na2O	0.250
Al2O3	17.500
SiO2	77.130

Volatiles

LOI

0.550

Links to Other Materials

Spodumene - Related
Amblygonite - Related
Lepidolite - Related
Cache

Miscellaneous

Family: Feldspar
Region: North America
Mined At: Unspecified
Raw Mineral: No
Generic: Yes

Notes

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 (lithium carbonate is soluble) 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 and imparts lower expansion and gives unique color response to copper and cobalt in glazes.

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. Flameware bodies can be made with 50-60% petalite.

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 an insoluble source 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.

A substitute for petalite can be made from 25% feldspar and 75% spodumene.

(Richard Willis)

Mineral, of the ideal form Li₂O, Al₂O₃, 8SiO₂with a typical empirical analysis of Li₂O 4.9%, Al₂O₃ 16.7%, SiO₂ 78.4%
Hardness: 6.5 Density: 2.4 Insoluble in water
A relatively stable (insoluble) and safe way of introducing lithium to a clay or glaze formula, where lithium’s “noble” manner of smoothing out “wrinkles” and an abundance of silica is desired. see spodumene

Data

Melting Point (MP): 1350C M
Co-efficient of Linear Expansion: 0.15
Specific Gravity: 2.45
Specific Gravity: 2.45
Co-efficient of Linear Expansion: 0.15
Melting Point (MP): 1350C M

URLs

Wikipedia definition - http://en.wikipedia.org/wiki/Petalite

Suppliers

Generic

Authors

Tony Hansen (Owner)

XML

<?xml version="1.0" encoding="UTF-8"?>
<material name="Petalite" descrip="" generic="1" rawmineral="0" searchkey="Lithium Feldspar" loi="0.55">
<families>
<family name="Feldspar"/>
</families>
<regions>
<region name="North America"/>
</regions>
<oxides>
<oxide symbol="Li2O" name="Lithium Oxide, Lithia" status="U" percent="4.320" tolerance=""/>
<oxide symbol="K2O" name="Potassium Oxide" status="U" percent="0.260" tolerance=""/>
<oxide symbol="Na2O" name="Sodium Oxide, Soda" status="U" percent="0.250" tolerance=""/>
<oxide symbol="Al2O3" name="Aluminum Oxide, Alumina" status="" percent="17.500" tolerance=""/>
<oxide symbol="SiO2" name="Silicon Dioxide, Silica" status="" percent="77.130" tolerance=""/>
</oxides>
<volatiles>
<volatile symbol="" name="" percent="0.550" tolerance=""/>
</volatiles>
<references>
<reference name="seealso" reason=""/>
<reference name="seealso" reason=""/>
<reference name="seealso" reason=""/>
</references>
<suppliers>
<supplier name="Generic" country="" url="" label=""/>
</suppliers>
<notes>
<note>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 (lithium carbonate is soluble) 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 and imparts lower expansion and gives unique color response to copper and cobalt in glazes.

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. Flameware bodies can be made with 50-60% petalite.

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 an insoluble source 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.

A substitute for petalite can be made from 25% feldspar and 75% spodumene.</note>
<note>Mineral, of the ideal form Li2O, Al2O3, 8SiO2 with a typical empirical analysis of Li2O 4.9%, Al2O3 16.7%, SiO2 78.4%
Hardness: 6.5 Density: 2.4 Insoluble in water
A relatively stable (insoluble) and safe way of introducing lithium to a clay or glaze formula, where lithium&#146;s &#147;noble&#148; manner of smoothing out &#147;wrinkles&#148; and an abundance of silica is desired. see spodumene

</note>
</notes>
<testdata>
<testitem testname="3" value="1350C M"/>
<testitem testname="3" value="0.15"/>
<testitem testname="3" value="2.45"/>
<testitem testname="3" value="2.45"/>
<testitem testname="3" value="0.15"/>
<testitem testname="3" value="1350C M"/>
</testdata>
</material>

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