I was wondering if anyone could shed some light on this for me. For the longest time I always thought that MDMA was a very fine almost powdery substance, and when I came across "Mollies" with glass looking shards in it I was quite astonished and blew it off as meth. Later on down the road I met a guy who confirmed for me that he once got MDMA that was big chunky crystals. Im just curious to know the actual science behind this , if any.
And also I was wondering if you can have other substances in a crystal shards like that, as in someone trying to scam saying they have pure MDMA shards.

Ive never seen fine shards MDMA, I think typically its more like the lumps cyb posted or like some of what you might find if looking for Quartz on google images. Pure MDMA is white/clear/opaque crystals, any color means an impurity, though the nature of impurity can vary, be benign or highly unwanted, and its impossible to judge by simply looking at it.

Any crystal when broken down fine enough will eventually look like powder.. MDMA, when in powder, usually has a more sugary granular consistence, as opposed to for example DMT which is more waxy or freebase harmalas which are more flour-like. I`m not really sure about meth but I can check.

Get a marquis reagent, meth and amphetamines will turn red/orange, while mdma will turn black. It wont tell you about impurities or mixed adulterations, for that you`d need a TLC kit, but at least with simple reagent you can prevent such obvious mislabellings such as meth for mdma.