jasper

Polished jasper pebble, one inch (2.5 cm) long.

Jasper that has not been polished.

Green Jasper.

Yellow Jasper. Can also be brighter and less brown.

Jasper, a form of Chalcedony ^[1] , is an opaque,^[2] impure variety of silica, usually red, yellow, brown or green in color. Blue is rare. This mineral breaks with a smooth surface, and is used for ornamentation or as a gemstone. It can be highly polished and is used for vases, seals, and at one time for snuff boxes. When the colors are in stripes or bands, it is called striped or banded jasper. Jaspilite is a banded iron formation rock that often has distinctive bands of jasper. Jasper is basically chert which owes its red color to iron(III) inclusions. The specific gravity of jasper is typically 2.5 to 2.9.^[3]

Etymology and history

The name means "spotted or speckled stone", and is derived via Greek iaspis, (feminine noun)^[4] from a Semitic language (cf. Hebrew yashepheh, Akkadian yashupu).

Green jasper was used to make bow drills in Mehrgarh between 4th-5th millennium BC.^[5] Jasper is known to have been a favourite gem in the ancient world; its name can be traced back in Hebrew, Assyrian, Persian, Greek and Latin.^[6] On Minoan Crete within present day Greece jasper was carved to produce seals circa 1800 BC based upon archaeological recoveries at the palace of Knossos.^[7]

The word yashepheh in the Masoretic text of Exodus 28:20, referring to a stone in the Hoshen, is thus reflected in the Septuagint by the word Iaspis, and usually translated into English as Jasper.^{[citation needed]} Despite the most common form of Jasper being red, scholars^[who?] think that the yashepheh here actually refers to a green form of Jasper - which was very rare, and so highly prized; the Greeks used Iaspis to refer to the green form, while the red form simply fell under the term Sard - which just means red.^{[citation needed]}

Types

Jasper is an opaque rock of virtually any color stemming from the mineral content of the original sediments or ash. Patterns arise during the consolidation process forming flow and depositional patterns in the original silica rich sediment or volcanic ash. Hydrothermal circulation is generally thought to be required in the formation of jasper.

Jasper can be modified by the diffusion of minerals along discontinuities providing the appearance of vegetative growth, i.e., dendritic. The original materials are often fractured and/or distorted, after deposition, into myriad beautiful patterns which are to be later filled with other colorful minerals. Weathering, with time, will create intensely colored superficial rinds.

The classification and naming of jasper presents an enormous challenge. Terms attributed to various well-defined materials includes the geographic locality where it is found, sometimes quite restricted such as "Bruneau" (a canyon) and "Lahontan" (a lake), rivers and even individual mountains, many are fanciful such as "Forest Fire" or "Rainbow", while others are descriptive such as "Autumn", "Porcelain" or "Dalmatian". A few are designated by the country of origin such as a Brown Egyptian or Red African leaving tremendous latitude as to what is called what.

Picture jaspers exhibit combinations of patterns (such as banding from flow or depositional patterns (from water or wind), dendritic or color variations) resulting in what appear to be scenes or images, on a cut section. Diffusion from a center produces a distinctive orbicular appearance, i.e., Leopard Skin Jasper, or linear banding from a fracture as seen in Leisegang Jasper. Healed, fragmented rock produces brecciated (broken) jasper. Examples of this can be seen at Llanddwyn Island in Wales.

See also

Wikimedia Commons has media related to: Jasper

• Carnelian

References