What is Jasper?
Jasper is an opaque variety of Chalcedony, and is usually associated with brown, yellow, or reddish colours, but may be used to describe other opaque colours of Chalcedony such as dark or mottled green, orange, and black. Jasper is almost always multicoloured, with unique colour patterns and habits.
Jasper, an aggregate of microgranular quartz and/or chalcedony and other mineral phases, is an opaque, impure variety of silica, usually red, yellow, brown or green in colour; and rarely blue. The common red colour is due to iron inclusions. The mineral aggregate 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 snuff boxes. The specific gravity of jasper is typically 2.5 to 2.9. Along with heliotrope (bloodstone), jasper (green with red spots) is one of the traditional birthstones for March. Jaspilite is a banded iron formation rock that often has distinctive bands of jasper.
History and Introduction
Jasper is one of the many gemstone varieties of quartz available today. It is an opaque and impure variety of silicon dioxide (SiO2). The name 'jasper' is derived from the Greek word for 'spotted stone', referring to its typical multicoloured, striped, spotted or flamed appearance. Jasper can form in virtually any colour. Jasper is usually considered a chalcedony, but some scientists classify jasper as a separate type because of its distinctive grainy structure.
Jasper is a dense substance, up to twenty percent of which can be made of foreign materials. Due to these trace impurities, jasper is rarely uniform. In some cases, jasper may even grow together with agate or opal. The patterns of jasper are formed during the process of mineral consolidation, determined by the exact flow and deposition of silica-rich sediments or volcanic ash. Jasper is often modified by other intruding impurities. As original deposits of silica materials naturally form with fissures and cracks after deposition, they are later filled by other minerals, such as iron oxide, manganese dioxide, metal oxide and sometimes organic matter. The final settling of these materials determines the specific appearance of the final substance.
The most common jasper patterns include interesting marbling and veining, orbital rings, streaks, spots, flaming and banding. Like agate stone, there are numerous trade names and classifications used for jasper today. The names can be very confusing, but fortunately, most are used only by the most avid collectors.
Types of jasper
Jasper is an opaque rock of virtually any colour 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 diverse patterns, which are later filled in with other colourful minerals. Weathering, with time, will create intensely coloured superficial rinds.
The classification and naming of jasper varieties presents a 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" or "porcelain". A few are designated by the place of origin such as a brown Egyptian or red African.
Picture jaspers exhibit combinations of patterns (such as banding from flow or depositional patterns (from water or wind), dendritic or colour variations) resulting in what appear to be scenes or images (on a cut section). Diffusion from a centre 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. While these "picture jasper" can be found all over the world, specific colours or patterns are unique, based upon the geographic region from which they originate. Oregon's Biggs jasper, and Bruneau jasper from Bruneau Canyon near the Bruneau River in Idaho are known as particularly fine examples. Other examples can be seen at Llanddwyn Island in Wales.
The term basanite has occasionally been used to refer to a variety of jasper, a black flinty or cherty jasper found in several New England states of the US. Such varieties of jasper are also informally known as lydian stone or lydite and have been used as touchstones in testing the purity of precious metal alloys.
Jasper is a variety of quartz with a chemical composition composed primarily of silicon dioxide. Up to 20% percent of fine dense jasper can be composed of foreign materials, typically hematite, pyrolusite, clay or calcite. It has such a distinctly grainy structure compared to other forms of chalcedony that some scientists even put jasper into its own individual group within the quartz family. Jasper has a microcrystalline structure which means its trigonal crystals can only be seen under high magnification. It can be easily distinguished from many other similar materials by its excellent hardness and lack of cleavage.
Jasper Origin and Gemstone Sources
Jasper gemstones can be found in many locations around the world. Some of the most notable deposits are sourced from Australia, Brazil, Canada, Egypt, India, Indonesia, Kazakhstan, Madagascar, Mexico, Russia, Uruguay, Venezuela and the United States of America, including Arizona, Arkansas, California, Idaho, Oregon, Texas and Washington.
Properties of Jasper
|Colour||White, Blue, Red, Green, Yellow, Orange, Brown, Gray, Black, Banded, Multicoloured|
|Hardness||6.5 - 7|
|Refractive Index||1.54 - 1.55|
|SG||2.63 - 2.65|
|Mineral Class||Quartz (Chalcedony).|