Re: Quartz?
- From: don findlay <don@xxxxxxxxxxxx>
- Date: Sun, 30 Dec 2007 19:07:03 -0800 (PST)
brad 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.
That was pretty good Brad. How did you go with the pre-ordering of
all the constituent bits of the Earth before accummulation?
------------------------------------------------------
You mean for the Earth there *was* no 'incandescence'? No
differentiation? Only accretion? ....The iron inner core accreted
first (from handy lumps of iron), then the outer core (also from handy
lumps of iron), then the mantle (from handy lumps of mantle), ..and
last of all the granitoid crust was last to accrete? (from handy lumps
of granite) Is that what you mean? That all these handy bits were
already pre-
sorted? And that all the rocky minerals were already created in small
'protoplanets' before the bombardment phase
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