Sorry to say - I'll plagiarize and show you a bit closer to the facts.

In Oxides and Hydroxides
Hematite Group
Corundum- Al2O3
Name: Probably derived from the Sanskrit, Kuruvinda, "ruby"; korundum.
Varieties: A very impure material, known as emery, is an intimate mixture of
granular corundum, magnetite, hematite and spinel.

So Emery is a variety of Corundum and happens to be the only entry in the book in this reference.

Spinel is MgAL2o4 it has a touch of Magnesium and another oxygen. Can be man made easily.
(and is in another group - the Spinel Group.)

Ruby add chromium for some of the Al. Not all. Sometimes the lesser ruby is Fe or Ti or now
FeTio3 all together.


Hematite is Fe2O3
Ilmenite is FeTiO3
Geikielite - MgTiO3
Pyophanite - MnTiO3

So as chemical elements - there are not exacts for this or that. Gemstones are mixtures
of alloys... And the names are the confusing issue. Different chemical content for the
same name simply due to local use, greed, or custom.....


What I slipped up on is truncating to much stuff and left off the 'emery'.

Martin

Martin Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder



Don Bruder wrote:
In article ,
"Martin H. Eastburn" wrote:


Corundum -- Al2O3 Hematite Group - Sapphire is a color type gem that isn't
red - ruby is red.
Other colors are sapphire - blue( star), black (star), yellow, ....
also known as corundum,


I'll buy that one, as I already know it's correct.


magnetite, hematite,


But not these two, which I know in both cases to be forms of iron, not
aluminum. Magnetite, in particular, is definitely ferrous - Under the
name of Lodestone, in association with a piece of string to hang it
from, or a cork and a bowl of water to float it with/on, it was
humanity's first compass needle. Except when used as a coil winding,
I've never heard of any form of aluminum exhibiting magnetic
properties... As for Hematite, I've heard it described, by several
different persons in positions to know, as "crystalized rust" because
it's essentially a lump of iron oxides with a handful of impurities.


and spinel.


Eh... Might be, but not sure, and not interested enough to find out.

Perhaps being classed in the "Hematite group" indicates they all have
similar crystal structures? They definitely don't have the same
molecular structures!


That is first year Mineralogy class. Useful when trading stones...


Mayhap someone needs to attend it...


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