Orbicular Jasper
   HOME

TheInfoList



OR:

Orbicular jasper is a variety of
jasper Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases, is an opaque, impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to ...
which contains variably-colored ''orbs'' or spherical inclusions or zones. In highly silicified
rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...
or
tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock co ...
,
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...
and
feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...
crystallize in radial aggregates of needle-like crystals which provide the basis or ''seed'' for the orbicular structure seen in this kind of jasper. The material is quite attractive when polished and is used as an ornamental stone or
gemstone A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or polished, is used to make jewellery, jewelry or other adornments. Certain Rock (geology), rocks (such ...
. Various local or commercial names have been used for the material, such as kinradite, oregonite, ocean jasper and poppy-patterned jasper, depending on the source. ''Poppy-patterned jasper'' or ''poppy jasper'' is the varietal name for material from several locations, but the most well known is from
Morgan Hill Morgan Hill is a city in Santa Clara County, California, at the southern tip of Silicon Valley in the San Francisco Bay Area. Morgan Hill is an affluent residential community, the seat of several high-tech companies, and a dining and recreation ...
,
Santa Clara County, California Santa Clara County, officially the County of Santa Clara, is the sixth-most populous county in the U.S. state of California, with a population of 1,936,259 as of the 2020 United States census, 2020 census. Santa Clara County and neighboring Sa ...
. The trade name Ocean Jasper is used for a variety found along the intertidal shores of northeast
Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...
. In
Nebraska Nebraska ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Ka ...
orbicular jasper is found in altered rhyolite beds noted for a variety of jaspers and related
agate Agate ( ) is a banded variety of chalcedony. Agate stones are characterized by alternating bands of different colored chalcedony and sometimes include macroscopic quartz. They are common in nature and can be found globally in a large number of d ...
s.


Gallery

File:Poppyjasper.jpg, Unpolished poppy jasper, Morgan Hill File:Jaspe orbiculaire Madagascar 1597.jpg, Madagascar orbicular jasper (detail)


References


External links


R. V. Dietrich – Gemrocks



Agate variety names – University of Nebraska-Lincoln
{{Morgan Hill, California Geology of California Jasper Morgan Hill, California