Rock Hard Carbide

Hard Rock cafe in Chicago is in the Carbide and Carbon Building, maybe a more appropriate name would be the “Rock Hard Cafe”? Carbides are fairly hard materials, and carbon, in the form of diamond is the hardest.

Hard Rock Cafe, Carbide and Carbon Building, Chicago.

Hard Rock Cafe, Carbide and Carbon Building, Chicago.

More info on one carbide (Fe3C cementite):
https://www.phase-trans.msm.cam.ac.uk/2003/Lattices/cementite.html

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Mohs’ Hardness Scale

Friedrich Mohs introduced a popular hardness scale to quantify hardness, mainly to help in identification of minerals and gems.

Mohs’ Scale Rosiwal-grinding-hardness Material for comparison
Graphite
1 Talcium 0.03
Lead, tin
2 Gypsium, rock salt 1.25
Aluminium, zinc, magnesium, copper, silver, gold
3 Calcite 4.5 Marble, brass, iron, nickel
4 Fluorspar 5
Steels unhardened
5 Apatite 6.5
Window glass
6 Feldspar 37
Low-carbon steels, hardened
7 Quartz 120
0.9% C steel, hardened; tungsten
8 Topaz 175
Special Steels
9 Corundum 1000
10 Diamond 14000

Mohs' Equipment

There are pictures of Moh’s scientific instruments on the phase transformations group web page. Prof. Harry Bhadeshia photographed the equipment which is on display in Graz.