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Mineral Introduction. Minerals: Building blocks of rocks. By definition a mineral is Naturally occurring (synthetic diamonds not a mineral) Inorganic solid Ordered internal molecular structure Definite chemical composition Rock A solid aggregate of minerals

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minerals building blocks of rocks
Minerals: Building blocks of rocks
  • By definition a mineral is
      • Naturally occurring

(synthetic diamonds not a mineral)

      • Inorganic solid
      • Ordered internal molecular structure
      • Definite chemical composition
  • Rock
      • A solid aggregate of minerals
      • Few rocks are composed almost entirely of one mineral – calcite
      • Obsidian & Pumice nonmineral matter both are crystalline glassy substances and coal – solid organic matter
most unusual mineral
Most unusual mineral?
  • The basic definition of a mineral is:
  • a material, composed of one or more chemical elements
  • with a definite crystal structure and a chemical composition which is either fixed or variable within identifiable limits

On this basis, ice is indeed a mineral: it is of hexagonal structure, of fundamental composition H2O, transparent and colourless, with Mohs hardness 1.5 and calculated specific gravity 0.917.

classification of mineral groups
Classification of Mineral groups
  • Nearly 4000 minerals have been named
  • Rock-forming minerals
      • Common minerals that make up most of the rocks of Earth’s crust
      • Only a few dozen members
      • Composed mainly of the 8 elements that make up > 98% of the continental crust
physical properties of minerals
Physical properties of minerals

Several physical properties are used to identify hand samples of minerals

Observation of minerals

Primary techniques:

Luster

Colour

Streak

Crystal Shape (habit)

Tenacity

Hardness

Cleavage

Fracture

Specific gravity (density)

Observation of minerals

Secondary techniques:

Taste

Feel

Smell

Double refraction

Chemical reaction to 10% HCL

luster
Luster
  • Appearance of a mineral in reflected light
  • Two basic categories
    • Metallic - submetallic
    • Nonmetallic - vitreous or glassy, silky, or earthy, greasy, pearly

Galena (PbS) displays metallic

Additionally the other optical property is the ability to transmit light,

No light is transmitted it is described as Opaque.

Light but no image is transmitted through a mineral it is said to be Translucent

Light and an image is transmitted through a mineral it is said to be Transparent

colour
Colour
  • Generally unreliable for mineral identification
  • Often highly variable due to slight changes in mineral chemistry
  • Exotic colorations of certain minerals produce gemstones

Quartz (SiO2) exhibits a variety of colours

Multicoloured tourmaline

streak
Streak
  • Color of a mineral in its powdered form
  • Streaking a sample can also help determine between metallic and nonmetallic,
  • Metallic minerals tend to have a dark streak whereas nonmetallic minerals tend to have a light streak
  • Hardness – if the mineral is harder than the streak plate = no streak
slide9

Habit – crystal shape

  • Refers to the common characteristics of shape of a crystal or an aggregate of crystals

Commonly used terms include

A equant (equidimensional) bladed flattened in one direction, fibrous, tabular

B prismatic faces that are parallel to a common direction

C banded stripes of bands of different colours and textures, platy, blocky

D botryoidalintergrown crystals representing a bunch of grapes

tenacity
Tenacity
  • Describes a minerals toughness or resistance to breaking or deforming
  • Some are BRITTLE such as the ionically bonded halite and fluorite, and these shatter when we hit them.
  • Minerals with metallic bonds such as native copper are MALLEABLE and are easily deformed and hammered into different shapes
  • Minerals that can be cut into thin shavings such as talc, gypsum are described as SECTILE
  • While others most notably the micas are ELASTIC as they will bend and snap back into their original shape once the pressure is released
mohs mineral hardness scale

1

5

9

2

6

10

3

7

4

8

Mohs Mineral Hardness Scale

Softest

1) Talc

2) Gypsum

3) Calcite

4) Fluorite

5) Apatite

6) Feldspar

7) Quartz

8) Topaz

9) Corundum

10) Diamond

All minerals are compared to a standard scale called the Mohs scale of hardness

Hardest

cleavage
Cleavage
  • Tendency to break along planes of weak bonding
  • Produces flat, shiny surfaces
  • Described by resulting geometric shapes
    • Number of planes
    • Angles between adjacent planes
common cleavage directions
Common cleavage directions

When minerals break evenly in one or more directions then they are described by the number of cleavage planes and angle(s) at which they meet

Fluorite, halite, and calcite all exhibit perfect cleavage

fracture density
Fracture & Density

Fracture

Absence of cleavage when a mineral

is broken

Density

Specific Gravity

Weight of a mineral / weight of an equal volume of water

Average value = 2.7

Most common minerals have a SG of between 2-3 Quartz has a SG of 2.65, the metallic mineral of Galena has a SG of roughly 7.5 and 24 karat gold has an SG of 20.

Quartz fractures into

a conchoidal pattern

physical properties of minerals1
Physical properties of minerals
  • Magnetism
  • Reaction to hydrochloric acid - Effervesce
  • Malleability
  • Double refraction
  • Taste
  • Smell
  • Elasticity
structure of minerals

Nicolas Steno

(1638-1676)

Structure of minerals

Law of Constancy of Interfacial Angles:

“angles between equivalent faces of crystals of the same mineral are always the same”

HOWEVER, minerals can be built of geometrically similar building blocks yet exhibit different external forms

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