G’day Ian, thank you for these details requested. I am surprised the Aussie Quarantine Dept. will allow mineral samples from outside Aussie via post without first irradiation, physical checks etc., before passage to addressee? I shall discuss this matter with our most experienced Geologist, then organise accordingly.
You will need a Certificate/document (from a lab/uni etc ) stating that the material :
1. is not soil…but an inert mineral sample like sand
2. was derived from below 6 m depth of cover
3. does not contain any organic/vegetative matter
4. that the sample is going to a mineral test lab for analysis.
Customs/Quarantine will open and inspect, usually.
Must keep weight below 20 kgs total for OHS reasons. So go for a 19kgs max wt.