Jasper
Opaque chalcedony full of other minerals — and it is the impurities that make it worth looking at.
Jasper is chalcedony made opaque by a high content of other material — commonly fifteen to twenty per cent, mostly iron oxides and clay. Where agate is valued for being translucent and banded, jasper is valued for being opaque and patterned, and the patterns come from exactly the impurities that would be considered contamination in another material.
Its density range is wider than the other quartz varieties for that reason: the figure depends on what else is in it.
The trade names are almost entirely descriptive and local rather than mineralogical — picture jasper, ocean jasper, orbicular jasper — and several materials sold as jasper are not chalcedony at all. It is the variety where nomenclature is loosest.
How to identify it
Opaque, quartz hardness, no cleavage, conchoidal fracture, and a dull to waxy lustre where agate is more vitreous. Opacity is the working distinction from agate and chalcedony, and a single specimen can be both.
Uses
Ornamental stone, cabochons, carvings, inlay and decorative panels. Historically as a seal stone and, in the Roman period, as decorative inlay and small vessels.
In the Neolithic and earlier, some jaspers were knapped as tool stone, which puts it in the same category as flint and chert — all three are cryptocrystalline silica selected for a conchoidal fracture.
Name origin
Through Latin and Greek from a Semitic root, and in antiquity the word was applied to a range of opaque coloured stones including some green ones that would now be called chalcedony or serpentine.
How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.
How this connects
Where a connection has been confirmed by an outside reference, that reference is named beside it.
is a variety of
- Quartz — mineral · chalcedony made opaque by fifteen to twenty per cent of other minerals, which are what give it its patterns
contains
- Iron — element · as oxide, and it is the impurities that make the material worth looking at
is used as
- Abrasive — application · knapped as tool stone in the Neolithic, for the same conchoidal fracture that flint and chert were selected for
is commonly confused with
- Agate — mineral variety · translucent against opaque, and a single specimen is often both — the boundary is a judgement rather than a composition
Sources
- Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
- Material WorldOur own writing