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Cornwall Stone
Chemistry
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Links to Other Materials
- Potash Feldspar - Alternative
- Soda Feldspar - Alternative
- DF Cornwall Stone - Related
- Cache
Hazards
- Cornwall Stone
Miscellaneous
- Family: Feldspar
- Region: Europe
- Mined At: Unspecified
- Raw Mineral: No
- Generic: Yes
Notes
Also know as: Pegmatite. Graven. Gowen. Manx stone. Meldon stone. Growan. Petunste. Amakusa.
Cornwall stone is a low iron feldspar material used primarily as a flux in clay bodies and glazes. It melts 1150-1300C. It has a more diversified selection of fluxes than other feldspars but also has one of the highest silica contents. It is popular in engobes for its adhesive power during and after firing and in glazes for its low shrinkage and minimal contribution to defects. The blue powdered material is higher in fluorine, the white is calcined and more refractory.
Its diversity of oxides make it similar in composition to common stone, thus its name. It is common to see synthetic substitutes for this material since it is easy to blend other feldspars to approximate the analysis of Cornish stone. These substitutes have the advantage of having no fluorine.
The parent ore materials are much more complex than other feldspars, and tend to be a mix of varying types of igneous rock in different stages of decomposition. Earlier stages of the ore materials are bluer (from fluorine) and contain more fluxes than newer rocks where some of the alkalis and fluorine have been leached and washed away creating a softer material. Cornish stones tend to be classified into major types according to the amount of flux present. Although Cornish stone is quite variable in composition, its low iron makes it an attractive material.
(Richard Willis)
Phylonian rock, a variety of pegmatite having a typical empirical analysis of SiO2 72.2%, Al2O3 16.1%, CaO 2.0%, K2O 4.06%, Fe2O3 0.23%, Na2O 4.12%, TiO2 0.05%, F 1.2%, MgO 0.04%, traces 1.4%
Also called “Cornish-stone” and “English China-stone”, one of the pegmatite feldspathics most resembling its granite origin. Very similar to Carolina stone, as a type of pegmatite. Used for off-white porcelain, and particularly as the feldspathic clay base for bone-china.
Linked Articles
Substituting Cornwall Stone
How to create a blend of materials to chemically substitute for another (Cornwall Stone is used as an example).
Suppliers
- Generic
Authors
- Tony Hansen (Owner)
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