Intrusive: Gems usually form in intrusive igneous rocks where the slow rate of cooling favors larger crystals.
intrusive igneous rock
Intrusive rocks are igneous rocks that have formed (and cooled slowly) beneath the surface of the Earth. These rocks usually have a coarse-grained or medium-grained texture, like granite.
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[edit] Intrusive igneous rocks
Intrusive igneous rocks are formed from magma that cools and solidifies within the earth. Surrounded by pre-existing rock (called country rock), the magma cools slowly, and as a result these rocks are coarse grained.
Intrusive, or plutonic igneous material is formed when magma fails to breach the surface, cooling slowly over millions of years to create an "intrusion.
Intrusive igneous rock composed of
dominant alkaline feldspar.
Xenolith -
Fragment of a rock included in another rock.
A coarse, intrusive igneous rock featuring extremely large crystals (some over 50mm in size).
intrusive igneous rock
Color: dark gray
Comments: contains plagioclase, anorthite, labradorite - bytownite, orthopyroxene, with some olivine, magnetite, ilmenite, apatite, chromite, and sulfide.
pluton An intrusive rock, as distinguished from the preexisting country rock that surrounds it. plutonic rock An intrusive rock formed inside the Earth crust, and individual crystal grains can be seen.
The heat of the intrusive igneous body and the hot volatile fluids serves to catalyze metamorphic reactions in the host rock. The incident fluids enhance ion mobility in the system and are highly reactive.
The fourth major mineral environment is hydrothermal, minerals precipitated from hot aqueous solutions associated with emplacement of intrusive igneous rocks.
It is also found in kimberlites " unusual intrusive rocks that contain diamonds. While most minerals have just one hardness, kyanite has a range of 4.5-6.
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The rock types are quite varied but always metamorphic or intrusive. They are mostly gneisses (complex migmatites), mica schists, quartzites and marble (which undoubtedly correspond to the original lithostratigraphic formations later metamorphosed), ...
Zircon is present in trace quantities in nearly all intrusive igneous rocks, particularly granites, where it occurs as very small crystals. Gem zircon is nearly restricted in occurrence to pegmatites or to quartz-poor, alkalic intrusive rock (e.g.
Skarn
the metamorphic rocks surrounding an igneous intrusive where the latter has come in contact with limestone or dolomite rocks
Spot price
current delivery price of a commodity traded in the spot market, also called the cash price ...
Recently, interesting minerals have been found in proximity to intrusive rocks, including prehnite and stilbite.
In similar paragenetic circumstances, in xenoliths, corundum "sapphire" variety, is also found, as well as spinel.
(1) With respect to a mine opening, the base or floor of the excavated area (stope); (2) With respect to intrusive rock, a tabular intrusive unit that is conformable with surrounding rock layers.
Slusher ...
kimberlite: an igneous rock of mantle origin occurring in intrusive breccia pipes, which is sometimes diamond bearing.
mantle: the ultramafic layer of the earth beneath the crust.
Hematite is generally considered helpful in shielding us from the emotions of others, but it can also help to shield us from our own intrusive thoughts. It is usually placed on the root chakra (base of spine).
-This area also produced rubies, sapphires and spinels from the detritus afforded by the disintegration of crystalline limestone surrounded by intrusive masses of granite. Neither ruby nor spinel appear to be abundant in this area.
Even non-intrusive work, such as appraisal for valuation, usually require that the jewellery be cleaned first.
When a basic wedding band or similar ring needs to be made a little smaller, the first method of choice is to compress it. Like its corresponding partner, stretching, this is fast, efficient and the least intrusive process.
Sugilite was first described in 1944 by the Japanese petrologist Ken-ichi Sugi (1901-1948) for an occurrence on Iwagi Islet, Japan where it is found in an aegirine syenite intrusive stock.
Natural pearls have no nucleus, but in the cultured variety the pearl is formed round a spherical bead inserted into the oyster shell. The oyster tries to render this intrusive body innocuous by sealing it off in a cyst of nacre.
 See also: Mineral, Crystal, Minerals, Color, Rock
  
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