Unreactive marble chips

Hi all

Recently bought marble chips 1-2mm for RoR experiments. But they have no reaction at all, even with 3M HCl.

Anyone know why this may be before I contact supplier? 16215104537956146931850596795264.jpg16215104693192348163779374781188.jpg
I agree they do look very similar to anti bumping granules. Wonder if somehow the supplier mixed them up (in which case I have a 1kg pack of them now!!). Tried with 2M nitric acid and there was nothing (put a larger chip in from other bottle and got vigorous reaction as expected). Can only conclude they are not marble chips...
It could be a trick of the light but the do look rather more sparkly than I would expect marble chips to be!
I have had this puzzle too. The marble chips of 3 different sizes bought before I started here did not react at all to acid of any concentration. I don't know how long they had been in school as previous techs did not date new stock on arrival. I had to buy all new chips.