Mine Development & Surveying

Mining Geology: Minerals & Rocks

How minerals are identified from physical properties and how the three rock families form — the geological vocabulary every MN question assumes.

PART 1

Topic Breakdown & Traps

The Engineering Principle

A mineral is a naturally occurring, inorganic, crystalline solid with a definite chemical composition; a rock is a solid aggregate of one or more minerals. Minerals are fingerprinted by physical properties — hardness (Mohs scale 1–10, talc to diamond), cleavage/fracture, lustre, streak (colour of the powder, far more reliable than the body colour), and specific gravity (SG). Rocks fall into three families by their mode of origin: igneous (crystallised from molten magma/lava), sedimentary (lithified from weathered detritus or chemical/organic precipitates, the host of coal and most placer/strata-bound deposits), and metamorphic (recrystallised in the solid state under heat and pressure).

The Core Formula Matrix

Specific gravity (Archimedes):

S G = \frac{W _{ai r}}{W _{ai r} - W _{w a t er}}

Density link:

ρ_{min er a l} = S G \times ρ_{w a t er} = S G \times 1000 kg/m^{3}

Mohs scale (ordinal, non-linear): talc 1, gypsum 2, calcite 3, fluorite 4, apatite 5, orthoclase 6, quartz 7, topaz 8, corundum 9, diamond 10.

Mineral mass in a rock:

m_{min er a l} = V_{r oc k} ρ_{r oc k} x_{min er a l}

(mass fraction

x

The ‘IIT Traps’

⚠
Streak ≠ colour. Body colour varies with impurities; the streak (powder colour) is diagnostic — e.g. pyrite is brassy but streaks greenish-black.
⚠
Mohs is ordinal, not linear. Diamond (10) is far more than twice as hard as apatite (5); never interpolate hardness numerically.
⚠
Rock vs mineral. Granite is a rock (quartz + feldspar + mica); quartz is a mineral. Coal, though organic, is classified with the sedimentary rocks.
⚠
SG uses the weight loss in water, not the water weight — the denominator is $W_{ai r} - W_{w a t er}$ .

PART 2

Progressive 3-Tier Question Suite

Q1BASIC1 Mark · MCQ

On the Mohs scale of hardness, the mineral that scratches all others but is scratched by none is:

Q2MEDIUM2 Marks · NAT

A mineral specimen weighs

54.0 g

in air and

34.0 g

when fully submerged in water. Its specific gravity is ______. (Round off to two decimal places.)

Q3HARD2 Marks · MSQ

Which of the following are correctly paired with their rock family? (Select all that apply.)