Jasper Chalcedony is a mineral with a hardness of 7 out of 10 on the Mohs scale of mineral hardness [?]. These Trigonally structured gems are made of silicon dioxide, their full chemical compound being SiO2.
Jasper is the opaque form of Chalcedony, the microcrystalline varieties of quartz that form concretionary deposits, partially of organic origin in the case of jasper.
It is commonly microscopically fibrous, massive, and has a nearly wax-like luster. It has a lower density than ordinary quartz.
It is the archetypal collectable beach pebble, dense, fine crystalline, translucent to opaque, and consists of massive, fine-grained quartz, fairly dense, containing significant amounts of other materials, particularly iron oxides.
Uniformly colored jasper is rare, usually it is multicolored, striped, spotted, or marbled. Most commonly, jasper is a dark brownish red but it may be yellow or black, green, grayish-blue, lavender, and brown, normally spotted or banded of impure variety of chalcedony or chert.
Jasper owes its range of colour from red through yellow to brown to admixed minerals.
Banded jasper is planar rather than concentric as agate. It has a dull to greasy luster. Fracture is uneven and angular. The various colors are caused by impurities of iron oxides. Finely divided hematite is responsible for the red colour and goethite for the brown and yellow colours. The presence of clay may give white, yellowish or greyish material with a porcellaneous appearance.
When the agent causing colour is present only in small quantities, jasper grades into a translucent fine-grained material for which the names chert, hornstone, and novaculite have been used.
The varieties are ribbon-jasper, which appear similar to agate in stripe bands or zones, Egyptian jasper, or orbicular jasper. The blue variety is called porcelain jasper.
Jasper, unlike agate and other chalcedonies, occurs as extensive beds of sedimentary or metamorphic origin. It grades into or is combined with other types of quartz which may traverse it or be combined with it as a breccia.
It is frequently found as patches in other stones that are called Blood stone or jasper agate. Irregular inclusions frequently create the impression of picture jasper or scenic jasper. Found in Utah, and Wyoming, USA, it could be a jasperized rhyolite.
It also occurs as a cavity filling or as nodules or veins in iron ores. It occurs in altered igneous rocks and in detrital deposits. Large-bedded deposits provide a good deal of ornamental jasper. It may occur in variegated red to brown colours as a petrifying agent of wood.
Deposits are found in Germany, Dauphine (France), India, and the Urals (Russia).
The difference between jasper, chalcedony, and agate is based upon the transparency of light. Jasper is an opaque variety, when the stone is translucent named as chalcedony, those translucent and bright colored stones are known as agate. A fine-grained, compact, velvet-black variety of chert into jasper, or flint named as Lydian stone, which are also called basanite, lydite, and touchstone.
Novaculite and hornstone are translucent varieties of jasper. An opaque, banded microcrystalline stone that is midway between onyx and jasper or chalcedony is known as jasponyx, ribbon jasper, striped jasper, or banded jasper.
It is also called jasperite, jaspis, jasperoid.
Jasper is derived from the old French "jaspre" meaning "spotted or speckled stone."
Jasper is known to have been a favorite gem in the ancient world as occurrences have been mentioned in Arabic, Persian, Hebrew, Assyrian, Greek and Latin.
In ancient Crete, jasper was worked to make seals, as in the palace at Knossos.
Often the porous chalcedony or jaspers are stained blue to imitate lapis lazuli and sold incorrectly as German lapis, or Swiss lapis.
Jaspilite, a banded variety of jasper occurs as metamorphic rock, which is alternated with hematite. It has a hardness near that of quartz. Used as ornaments, beads, cut cabochon, buttons, brooches, and to simulate cameo.
Orbicular varieties and jaspers displaying spherules of different colours are used as ornaments.
Examples of trade names for jasper include basanite, plasma, silex.