Not enough info on these for anyone say based on the photos alone.
Start with a hardness test, try and scratch them with a nail or knife or try to scratch some glass with them. Do a streak test, rub/scrape them against a white unglazed porcelain tile or something similar. Put some drops of vinegar or better yet muratic/hydrochloric acid on them (with care) and look for fizzing or bubbles. put a magnet to them, see if it sticks. crack them in half and take a close up photo of the fresh surface and then post them here.
If you do some or all of those things we may be able to at least narrow down what you have there.