XRD: Determines crystal structure (eg minerals) eg Feldspars, Quartz, Mica, Kaolin - Destructive method as the material needs to be milled and pressed into a slide to feed the machine. Ideal sample size 1/2 - 1 teaspoon
XRF: Is for elements, such as lead, gold, titanium etc - Depending on sample, may need to have bits chipped/scraped off to fit in the sample chamber. Rings and coins etc go in whole. Need 1/2 teaspoon of material ideally to form a pellet, but can get by with smaller amounts, but not as accurate. Max size for single object 30mmx30mmx30mm
Pycnometer: Allows you to calculate material density by displacement of water. Mixtures of material, eg gold in quartz, quartz matrix with voids etc will increase error margins. Sample size 20mm max from memory. Haven’t dug it out of the back storeroom yet.