Re: Quartz?
- From: brad <lbjohnson1949@xxxxxxxxx>
- Date: Tue, 1 Jan 2008 09:39:56 -0800 (PST)
On Jan 1, 12:03 am, KC <koh...@xxxxxxxxxxx> wrote:
On Dec 30, 6:34 pm, brad <lbjohnson1...@xxxxxxxxx> wrote:
On Dec 30, 6:16 pm, KC <koh...@xxxxxxxxxxx> wrote:
I have read that gold and emeralds are often found in, or near, veins
of quartz. The reasons for emeralds being found there is
understandable since both are crystal formations, but why is gold
found with quartz? What do the two have in common?
KC
you must know first that Si and O are the 2 most abundant elements in
the crust. so any igneous intrusion contains oxides of silica. in
addition water is common in the crust. water associated with magma is
extremely hot, and deep in the crust will be at very high pressure .
hot water under high pressure will readily dissolve metals , in fact
seawater contains dissolved metals. if you have a melt saturated with
SiO2 , quartz will be the primary mineral associated with that
deposit, if Be and Al are also present emeralds may also be present.
if that melt also contains water saturated with dissolved metals it
may be intruded into cracks and as the water (steam) condenses may
deposit Au, Ag,Cu in those places as it cools and depressurizes. these
deposits are called hydrothermal deposits. this is a very simplified
explanation but it comprizes the gist of the process. Native
minerals , as an ore, are always found in hydrothermal deposits. and
since Au, Ag, and Cu all have the same valence they are common
together as mixtures so that if you find one most likely the others
are also present though not necessarily in equal measures.
Thanks. If quartz is the 2nd most common mineral, can I assume that
it does not take a melt to form it? And if that is true, is there any
difference between quartz found in a hydrothermal vent and quartz
found loose on the surface?
KC- Hide quoted text -
- Show quoted text -
the word quartz refers to its genesis only . SiO2 can form other
minerals (glass - no crystalline structure and technically not a
mineral) opal, tridimite, cristobalite, coesite, stishovite,
lechatelierite. you can,t infer that quartz is the 2nd most common
mineral , although silicates as a group make up 1/3 of all mineral
species and maybe 90% of the crust. quartz found loose is weathered by
erosion from somewhere else, and redeposited. and may be identical to
igneous generated type. however , well sorted sediment high in silica
( dunes, beaches ) weathered out of any number of silicate minerals
may be reburied , subjected to high temperature and pressure,and that
rock will be quartzite with structure ranging from glassy to
crystalline depending on the amount of metamorphism. you must
consider the relationship of the mineral to its surroundings as well
to determine which one you have . in addition other elements present
may be bound to the SiO2 and form entirely new minerals if the
metamorphism is severe enough.
.
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