Environmental Engineering Reference
In-Depth Information
or the ease of carving. Friedrich von Mohs [MOH 25] noted as early as 1825 that
minerals of different origins could have the same hardness. In the scale that he
conceived, named after him, 10 common minerals are classified according to
arbitrary units ranging from 1 to 10 (see Table 8.3).
Since that time, other systems have been proposed based on measurements of
indentation. The most common sclerometers, exclusively reserved for laboratory
measurements, are those of Brinnel, Vickers, Knoop and Shore; the way they are
used is detailed in [WIN 94].
Hardness
Mineral
Tool (hardness)
Other substances
1
Talc
Nail (2 ½)
Graphite
2
Gypsum
Nail (2 ½)
Epsomite, kaolinite, copper
3
Calcite
Copper alloy coin (3 ¼) Anhydrite, iron with low carbon
content, copper
4
Fluorite
Glass lamella (5 ½)
Dolomite, siderite
5
Apatite
Glass lamella (5 ½)
Magnetite, goethite
6
Feldspar
Steel blade (6 ¼)
Hornblende, augite, hematite, pyrite
7
Quartz
Corundum (9)
Some ceramics, carbon-rich steel
8
Topaze
-
Silicium carbide, carborundum
9
Corundum
-
10
Diamond
-
Triboric nitride
Table 8.3.
The most common minerals on the Mohs scale [WIN 94]
In desert countries, such as Egypt, abrasion phenomena are frequent due to the
occurrence of sand storms. In temperate regions, erosion features are mainly linked
to human interventions such as mechanical cleaning by abrasive powders or metal
tools. Backpacks scratching on walls in monuments visited by tourists, polishing of
pavement stones by the repeated abrasion effect of feet or cars are other frequent
mechanical degradations.
