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Orbicular jasper from Madagascar. Orbicular jasper is a variety of jasper which contains variably-colored orbs or spherical inclusions or zones. In highly silicified rhyolite or tuff, quartz and feldspar crystallize in radial aggregates of needle-like crystals which provide the basis or seed for the orbicular structure seen in this kind of jasper. [1]
Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases, [1] [2] is an opaque, [3] impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to iron(III) inclusions. Jasper breaks with a smooth surface and is used for ornamentation or as ...
Biggs jasper is a variety of the mineral jasper. It is a "picture jasper" – a jasper that exhibits particular patterns and colors – and is used as an opaque gemstone . [ 1 ] It exhibits intricate, shell- or layer-like patterns in shades of brown ranging from beige to dark brown.
Slabs can either penetrate directly into the lower mantle, or can be retarded due to the phase transition at 660 km depth creating a difference in buoyancy. An increase in retrograde trench migration (slab rollback) (2–4 cm/yr) is a result of flattened slabs at the 660-km discontinuity where the slab does not penetrate into the lower mantle. [38]
Two medieval grave slabs — dating back nearly 800 years — were recently recovered from the ocean floor off the United Kingdom, researchers said. ...
Thunderbird Archaeological District and Jasper quarry, near Limeton, Virginia, is an archaeological district described as consisting of "three sites—Thunderbird Site, the Fifty Site, and the Fifty Bog. It is located in Warren County Virginia, near modern-day Front Royal, in the Shenandoah River Valley.
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The motivating force for seafloor spreading ridges is tectonic plate slab pull at subduction zones, rather than magma pressure, although there is typically significant magma activity at spreading ridges. [3] Plates that are not subducting are driven by gravity sliding off the elevated mid-ocean ridges a process called ridge push. [4]
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