Porcellanite

A group of siliceous-rocks that have the texture, lustre and conchoidal fracture of porcelain. A dense siliceous rock having the texture, dull luster, hardness, conchoidal fracture, and general appearance of unglazed porcelain; it is less tough, dense, and vitreous than chert.

The term has been used for:
1. an impure chert, in part argillaceous;
2. an indurated or baked clay or shale often found in the roof or floor of a burned-out coal seam, see porcellanite (metamorphic).
3. a fine-grained, acidic Tuff cemented by secondary silica.
and
4. A silicified radiolarite

The first definition is most generally used.

According to Grapes (2006) porcellanite is a pyrometamorphic rock that is a very fine-grained, light-coloured, completely recrystallized clay, marl, shale, or bauxitic lithomarl.

Also spelled: porcelanite; porcelainite.

See Also: siliceous shale, Porcelain Jasper, haelleflinta, clinker

The names "porcelain-jasper", "porzellanjaspis", and "basaltjaspis" are inadequate.

Ref: AGI