Looking for multi-phase mineral specimen with small domains

[bamajon1974]

Good afternoon. New user on Probe Software forums. Reasonably experienced SEM/microanalysis user. My expertise lies more in metals, metal alloys, and intermetallics, not geological samples.

I am looking for a mineral specimen with multiple phases where the domain sizes are small (100s of nm to 10s of microns) and more or less homogeneously distributed so most of the phases can be shown in one image at modest magnifications, for training and demonstrating purposes. I have found specimens with multiple sulfide phases (zinc, lead, copper, iron) present but the domains are fairly large (mm size) which makes showing multiple phases in one image difficult, even at base mag. Not just limited to sulfides but any specimens that meet the criteria will work.

Ebay has tons of mineral specimens but it is difficult to know what the sizes of phase regions in the interior by just looking at a few pictures and little knowledge of the sample. I am fine with purchasing samples too. Probably not borrowing as I would like samples to keep.

I have access to a metallography lab with cutting saws, vibratory polishers, and hot expoxy mount techniques as well as carbon coaters and metal evaporators. Prepared thin sections or rocks out of the ground are fine.

In other places, it was also suggested I also prepare my own samples, something I didn't consider. Perhaps homogenizing several metal oxides, pressing into pellets, and them imaging/analyzing. Are there any specific protocols for sample preparation to recommend?

Thanks!

[crystalgrower]

In general you want to be looking for "sintered" materials whose grain size will be close to your desired range, and SEM images will show empty space around the grains.  CeO2, ThO2, LaB6.

Rare earth silicides which are called RSi2 on the label  are a mix of R3Si5 and Si-rich micron sized areas.

For natural minerals the tugtupite sold on ebay will usually be a mass of micron sized crystals. 

You could also contact Turnstone Geological Services Limited.  Graham Wilson has a collection of very unusual pegmatites and will be the best person to direct you. 

[crystalgrower]

Other mineral specimens to look for at rock shops or Ebay:

-"-unakite" intergrown epidote and feldspar and quartz, look for finely intergrown green and orange grains

--the Precambrian granite pebbles that are widespread across Eastern North America, sub-mm intergrown grains of quarztite feldspar and biotite.  If you are in the area look for glaciar-polished pebbles in "gravel" at a builders supply.  Or in a streambed or on the beach...

In contrast most calcite-dolomite mixes are too coarse grained.

[bamajon1974]

(bump) any other suggestions?

[Ben Buse]

A mineral displaying an exsolution texture? e.g. Ilmenite contained exsolution lamella or perthite

Although it might be a bit hit and miss as to whether texture present.

Or maybe a volcanic rock is more what your after - with glass containing microlites and quench textures, a basalt or rhyolite? Although between groundmass areas will be larger phenocrysts

[crystalgrower]

(bump) any other suggestions?

Please use your internet browser of choice to connect to Turnstone Geological Services.  Use a laptop or desktop because the format was created to be optimized for full screens.  There are more than 270 examples.  Please remember that a pegmatite will have areas of fine grains and areas of coarse grains. 

Then use your browser of choice to search for (mineral) and (specimen) and (place of origin) if it is important.  Reliable providers will always post photos with a scale or indication of dimension (sometimes verbal).  You can contact individual sellers for more specific information such as grain size.  Ebay listings will also include some scale or the seller can be contacted.