Jasper
From Wikipedia, the free encyclopedia
- This article is about the mineral. For other uses see Jasper (disambiguation)
Jasper is an opaque,[1] impure variety of silica, usually red, yellow or brown in color. 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.[2]
Contents |
[edit] Etymology and history
The name means "spotted stone", and is derived from Anglo-French jaspre, from Old French jaspe, from Latin iaspidem, the accusative of iaspis, from Greek iaspis, via a Semitic language (cf. Hebrew yashepheh, Akkadian yashupu), ultimately from Persian yashp.
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.[3] On Minoan Crete within present day Greece jasper was carved to produce seals circa 1800 BC based upon archaoelogical recoveries at the palace of Knossos.[4]
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. Despite the most common form of Jasper being red, scholars 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. Rebbenu Bachya argues that this stone represents the tribe of Benjamin, but there is actually a wide range of views among traditional sources about which tribe the stone refers to.
It is described in the Book of Revelation (21:11) as follows: "It shone with the glory of God, and its brilliance was like that of a very precious jewel, like a jasper, clear as crystal."
[edit] Types of jasper
Jasper can appear as an opaque rock of shades of red due to mineral impurities. Patterns can arise from the formation process and from flow patterns in the sediment or volcanic ash that was saturated with silica to form jasper, yielding bands or swirls in the rock.
Jasper may be permeated by dendritic minerals providing the appearance of vegetative growths. The jasper may have been fractured and/or distorted after formation, later rebonding into discontinuous patterns or filling with another material. Heat or environmental factors may have created surface rinds (such as varnish) or interior stresses leading to fracturing.
A brown jasper that occurs as nodules in the Libyan desert and in the Nile valley is known as Egyptian jasper or Egyptian pebble.
Picture jaspers simultaneously exhibit several of these variations (such as banding, flow patterns, dendrites or color variations) resulting in what appear to be scenes or images in a cut section. Spherical flow patterns produce a distinctive orbicular appearance. Complex mixes of impurities produce color variations. Healed fractures produce brecciated jasper. Examples of this can be seen at Llanddwyn Island.
Another type of Jasper is Leopard Jasper, also known as Orbicular Jasper. It is composed primarily of silicon dioxide (SiO2) and is a variety of Chalcedony, a type of quartz. Leopard jasper is usually an opaque combination of tan, gray, black or reddish-brown circles or 'spots' of color, hence its name.
[edit] See also
[edit] References
- ^ Mindat: Jasper profile
- ^ R. V. Dietrich, Gemrocks
- ^ [*http://www.gemstone.org/gem-by-gem/english/jasper.html International Colored Gemstoen Association: Jasper]
- ^ C. Michael Hogan, Knossos fieldnotes, Modern Antiquarian (2007)
|
|||||||||||||||||
|
||||||||||||||||||||||||||||
