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Review key What Is the Mohs Scale and How Does It Measure Mineral Hardness? exam facts and rate your mastery to track revision.
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#1
The Mohs scale is a qualitative ordinal scale that measures the relative scratch resistance of minerals on a scale from 1 to 10.
#2
The scale was devised in 1812 by German geologist and mineralogist Friedrich Mohs to assist in field identification of minerals.
#3
Mineral hardness reflects the strength and density of atomic bonds forming the crystal lattice structure.
#4
Talc is the softest reference mineral on the Mohs scale, assigned a hardness rating of 1.
#5
Gypsum is the reference mineral for hardness 2, easily scratched by a human fingernail.
#6
Calcite, a carbonate mineral forming limestone and marble, acts as the standard for hardness 3.
#7
Fluorite represents hardness 4, and apatite, a phosphate mineral found in tooth enamel, represents hardness 5.
#8
Orthoclase feldspar, an abundant potassium tectosilicate, represents hardness 6.
#9
Quartz, consisting of silicon dioxide (SiO2), is the benchmark for hardness 7.
#10
Topaz represents hardness 8, and corundum (aluminum oxide, forming ruby and sapphire) represents hardness 9.
#11
Diamond, a cubic allotrope of carbon, is the hardest naturally occurring mineral, assigned the maximum rating of 10.
#12
Common field testing tools include a human fingernail (~2.5), a copper coin (~3.0), a pocketknife blade (~5.5), and a streak plate (~6.5 to 7.0).
#13
The Mohs scale is purely ordinal (relative ranking), not a proportional or linear quantitative scale.
#14
On the absolute Knoop micro-indentation scale, diamond (~8,000 kg/mm²) is more than four times harder than corundum (~2,000 kg/mm²).
#15
The leap in absolute hardness from corundum (9) to diamond (10) exceeds the cumulative difference between talc (1) and corundum (9).
#16
Hardness measures resistance to surface scratching, whereas toughness measures resistance to fracturing or breaking under mechanical impact.
#17
Despite its maximum hardness, diamond exhibits perfect octahedral cleavage, meaning it can shatter easily along structural planes if struck.
#18
Lonsdaleite (hexagonal diamond) and aggregated diamond nanorods are theoretical carbon allotropes that exceed standard diamond hardness.
#19
Minerals can display directional hardness: kyanite exhibits a hardness of 4.5 along its length but 7.0 across its width.
#20
In gemstone cutting and jewelry crafting, minerals with a Mohs hardness below 7 are susceptible to scratches from ordinary quartz airborne dust.
Subject Specialist Commentary
Analytical perspective & practical exam advice from the Master10 academic board
Devised in 1812 by German mineralogist Friedrich Mohs, the Mohs scale ranks minerals from 1 to 10 based on their scratch resistance. Hardness reflects how strongly atoms are bonded within a mineral's crystal structure. The scale uses ten reference minerals: talc is the softest at 1, gypsum ranks at 2, quartz sits at 7, and diamond tops the scale at 10 because it can scratch every other natural substance.
In SSC and State PSC examinations, students often fall into the trap of assuming the Mohs scale is linear. It is purely an ordinal ranking; absolute testing shows the hardness leap from corundum (9) to diamond (10) is greater than the entire difference from talc (1) to corundum (9). Remember common field scratch testers for rapid prelims questions: a fingernail measures about 2.5, a copper coin is 3.0, and a pocketknife blade is roughly 5.5.
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