Could somebody tell me what this is

[Addz]

 

[user 4485]

More than likely quartz.
To be 100% would need more information as per:
https://www.prospectingaustralia.com/forum/viewtopic.php?id=24758

 

[grubstake]

If you mean the stone overall, it's almost certainly just quartz, as mbasko has said. :gemstone:

If you mean the tiny rainbow, that's a prism effect caused by a crack within the stone. :rainbow:

If you mean the badly-bitten fingernail, that's caused by a bad habit that you might grow out of. layful:

 

[user 4386]

Yes, the form of the crystal indicates that it is probably quartz. Hardness alone should tell you.

 

[RockRat]

A smokey quartz with the same effect. good find :gemstone: