Spinel standards

[JohnF]

I am looking for a spinel (MgAl2O4) epma standard. Anyone have something to share?

[Probeman]

I am looking for a spinel (MgAl2O4) epma standard. Anyone have something to share?

Hi John,
I have a lot of this wollastonite:

http://smf.probesoftware.com/index.php?topic=222.msg997#msg997

Good for major silicon and aluminum.

[JohnF]

I think you meant Si and Ca (no Al in wollastonite, CaSiO3)

[John Donovan]

I think you meant Si and Ca (no Al in wollastonite, CaSiO3)

Yes, sorry. I ain't no darn geologist!

But that does remind me: I'd love to find a super pure end member aluminum silicate, such as sillimanite.

[Gseward]

JohnF and I discussed this off-line. We discovered this:

http://www.mtixtl.com/mgal2o4spinel.aspx

[Jeremy Wykes]

A heads up on synthetic Mg-Al spinel: If I remember correctly, Hugh O'Neill suggests that synthetic MgAl2O4 he has examined in the past has considerable non-stoichiometry.

[Gseward]

Thanks for the warning. I guess heterogeneity is worse!

[Probeman]

A heads up on synthetic Mg-Al spinel: If I remember correctly, Hugh O'Neill suggests that synthetic MgAl2O4 he has examined in the past has considerable non-stoichiometry.

Would that be true even for single crystal material?  I believe Sean Mulcahy (UB Berkekey) has single crystal Mg-Al spinel from when I bought it years ago.  Worth testing I guess.

[AndrewLocock]

We purchased a large polished single-crystal wafer (substrate for crystal growth) of MgAl2O4 spinel from MTI some time ago. My recollection is that examined the cell dimension by powder XRD of an aliquot, and found it to be in excellent agreement with ideal MgAl2O4. From this, we assumed the composition was stoichiometric.