Sounds pretty hard. I can only guess that the matrix rock is an igneous type lava that came in contact with those crystals when it was molten, as they don't look to have formed in that rock imo. Diamonds are found in a igneous type rock called Kimberlite, check out those images... Every time I think I find a thrift store piece of jewelry with a possible diamond I run up to the pawn shop and they touch it with their tester. It works I think on how fast the element conducts heat. See what that tester does on that crystal. I found a diamond that was the color of green tea about the size of a BB panning in a Colorado mountain stream. I took it to the Jeweler in Salida Colorado and his heat tester beeped good on it. I don't know now what I did with it. It could still be around in some of the stash places of mine or I left it with the shack-up from those days, as it was in the early 1980's when I found it. I do remember where I found it and the type of underlying layer I washed it from. Some day I hope to go back and see if I can relocate that special layer of stuff again and maybe find some more. I don't have a bucket list. I have a someday list.
The first two pictures is the rock that contained the transparent mineral I'm holding with the blue glove..now the rock has many tiny Stones in it that appear to be Little diamonds. The mineral I'm holding with the blue glove , is very slippery almost oily like, I used a Dremel with a tungsten carbide bit to see what it would do to the mineral and to my surprise The tungsten Dremel bit lost most of its rough grip... And the mineral remained the same
