Inspired by this comment, I wonder, what materials have LEGO Bricks been made out of, apart from plastic? Can these also interlock with other blocks?
Ignoring the different kinds of plastic that LEGO have used for their bricks over the years (formerly CA, HIPS, Bakelite, PC - currently (M)ABS - and a range of different plastic types for parts that need different properties), I can't think of any bricks that came with LEGO sets that fit your criteria.
If we expand the scope to the gear category (things like key chains, clothing, storage solutions, etc. with the LEGO brand), there are a few that seem to fit your criteria. The ones I can think of :
- 14 Karat Gold Brick made of 14-karat gold
- 2 x 4 Brick - Sterling Silver (925) Key Chain made of Sterling silver 925
- Eraser, 2 x 4 Brick with 3 Holes on Bottom - unsure what it's made of - likely some synthetic rubber or gum (which you might label as "plastic", in which case it doesn't match your criteria)
I have none of these, so can't attest to their ability to interlock with regular bricks, nor to their clutch power. I also haven't been able to find information on this (the former two are very rare).