Help id these little crystals

[Rivarat]

I found these a few years ago.
They are small at best they are about the size of a pin head, but I have a new toy - a mircoscope, it brings out a whole new world.
They are heavy they were all in the bottom of the pan.
They don't seam to be magnetic.
The area they came from is in north east Vic. not known for anything, although there are sapphires and zircons about 15km away as the crow flies.
I won't say just were yet, as we did find a nice little blue sapphire (about twice the size of a matchhead) with these crystals, but haven't been back yet with the sieves.

These are tiny crystals the photos are at 60x resolution

 

[WalnLiz]

Black Spinels....come quite a bit larger than those and polish up extremely well for jewellery. If they're in the area quite often Sapphires, Zircons and Garnets aren't far away.

Wal.

 

[rough2cut]

If you can scratch them with a sapphire they are spinel if they scratch the sapphire they are diamond.

 

[user 1769]

There are a few black minerals like that. They could be pleonaste spinels, or blackjack, as Wal says. But other black minerals in the spinel family like magnetite and particularly chromite also form crystals like that. If the area contains any ultramafic geology, especially serpentine, I'd put my money on chromite.

 

[Rivarat]

I never even thought of spinel, seems to tie in with the sapphire from there too. Just haven't even seen them in the crystal form before just black globs where I normally look for sapphires and zircons.
If only I could find some a bit larger I could try a scratch test.
Looks like I might have a new sapphire spot to check out further, might be relatively untouched as there has been no mining in that area, I have no idea why we were even sampling in that creek.

 

[Rivarat]

Some companies have explored there in the past nut no mining
Here's a couple of extracts from report from Geovic on the area which might help

Geochemistry - The location of various prospects investigated in detail are presented in Figure 2. A
reconnaissance drainage sampling programme, with 71 samples being taken, was conducted in early 1991. At
each site approximately 5 kg of -2 mm active drainage sediment was sieved on site. Subsequently, a -80# sample
was dry sieved off each -2 mm sample. The remaining -2 mm sample was analysed by BCL for Au with a peak
value of 52.4 ppb Au returned. Peak results for the -80# stream sediment samples in ppm (unless otherwise stated)
are as follows:

Au 21 Cu 140 Pb 35 Zn 150 Ag <1 As 38 Sb 5 Fe% 9.68
Co 75 Cr 300 Ni 120 Mn 3450 P 1150 S 540 V 330

Bulk stream sediment samples weighing 2 to 3 kg were collected and sieved to -180mm. Cambrian greenstone
areas were sampled at a density of about 1 sample per 3 square km. Thresholds were defined as 100 ppm copper,
100 ppm zinc and 50 ppm nickel. Only one sample proved anomalous in all three elements. Such minerals as
almandine, andrasite, apatite, augite, biotite, chlorite, epidote, hornblende, hydrogrossular, ilmenite, monazite,
pumpellyite, rutile, tourmaline and zircon were identified in the heavy metal concentrates of the samples
collected. Gold and platinum were absent from all samples. Peak stream sediment results are as follows (ppm):