Chemical Formula : CSi 

Mohs Scale : 9, 9.5

Crystal System : Hexagonal 

Chemical Formula : Bi, BiO2

Crystal System : Rhombohedral

Melting Point : 271.5 °C 

• Bismuth is a are metal that is solid at room temperature. It is more rare than platinum, ranking number 69 out of the 75 listed rare elements found on Earth's crust. Bismuth is a crystalline white metal that is still solid at room temperature, however, it doesn’t take much to melt it. Once molten, after the bismuth cools back down, it organizes its molecules into really interesting shapes. The iridescent coloring is due to a thin layer of bismuth oxide that forms on the surface of the crystal as it cools 

Chemical Formula : CuSO4·5H2O 

Mohs Scale : 2.5

Crystal System : Triclinic

Chemical Formula : Si

Mohs Scale : 6.5

Crystal System : FCC 

Chemical Formula : Mg

Mohs Scale : 1 - 2.5

Crystal System : Hexagonal