1. Mineral Introduction
Cube Fluorite

2. 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
What is a mineral? ASK CLASS
Geologists define a mineral as any naturally occurring inorganic solid that possesses an orderly crystaline structure and well defined chemical composition.
READ SLIDE
Inorganic solid halite are found naturally in the ground and are minerals, what other substance on your table has a crystalline structure? Sugar, but this is considered organic and therefore not a inorganic solid. Shells secreted by animals are considered inorganic
Ordered internal molecular structure, their atoms are aligned or arranged in an orderly manner and have a regular shape quartz.
Chemical compounds, pyrite FeS2 consists of one iron atom and two sulfur atoms
Ice is a great substance, as some of you know I am a fan of water and ice, but another amazing thing about ice is that because minerals are solids within temperature ranges found on the planets surface, and thus ice is considered a mineral, liquid and gas water are not.
Rock is defined as a solid mass of minerals or mineral like matter that occur on our planet.
Few rocks are composed almost entirely of one mineral – limestone is an example made from impure masses of calcite
HOWEVER most rocks are more common as AGGREGATES of several kinds of minerals, the term aggregate implies that the minerals are joined in such a way that that the properties of each mineral are retained.

3. 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
What kind of mineral do you think this is?
Most people would probably not think of ice as a mineral. However, many of us have seen magnified images of delicate snow flakes, and the typical six-sided form, even though much embellished by finer structures, is evidence of internal order.
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
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

4. 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
So now that we know how to identify the minerals, how do they get named and classified?
READ SLIDE
Ones we will need to know about are the rock forming minerals
Is interesting to note that 8 elements make up the bulk of the rock forming minerals, and reprsent over 98% (by weight) of the continental crust. In order of abundance oxygen, Silicon, aluminum, iron, calcium, sodium, potassium, and magnesium.

5. 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
Each mineral has a unique crystalline and chemical composition which give it its unique properties, such as hardness, density, appearance etc and several physical properties can be used to identify hand samples of minerals
Primary techniques READ SLIDE
For some minerals there are a few secondary techniques – READ SLIDE

6. 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
The appearance or quality of light reflected off a mineral is known as luster.
There are 2 types Metallic and nonmetalic, minerals that appear metal regardless of colour are said to be metallic.
Some minerals which initially appear to be metallic have a reaction with the atmosphere, such as copper of galena and become dull or tarnished and these are then classified as having a submetallic appearance.
Most minerals have a nonmetallic luster, and are described by using adjectives such as vitreous or glassy, silky or earthy, greasy or pearly (like a pearl)
Additionally the other optical property is the ability to transmit light, when no light is transmitted it is described as Opaque.
When light is transmitted but no image is transmitted through a mineral it is said to be TRANSLUCENT
When light and an image is transmitted through a mineral it is said to be transparent.
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

7. Quartz (SiO2) exhibits a variety of colours
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
Even though colour is the most conspicuous characteristic of any mineral it is considered to be a diagnostic property of only a few minerals
Any slight impurity within the mineral composition can give it a different colours
Additionally other minerals such as tourmaline often display various hues with multiple colours sometimes being present in the same sample
Multicoloured tourmaline

8. 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
No visual colour of a mineral may not always be diagnostic, but the colour of the powdered mineral often is and this is known as streak.
This is achieved by rubbing the mineral across a plate and seeing what colour it is. A useful diagnostic tool
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
Be careful when streaking as it can be a difficult thing to pull off and often get you arrested

9. 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 botryoidal intergrown crystals representing a bunch of grapes
The term habit is used to refer to the common characteristics of shape of a crystal or an aggregate of crystals
Using habit is useful if you remember that some minerals exhibit specific shapes, READ SLIDE, and some like halite are cubic form, but others we must use other diagnostic features as they have more than one characteristic form like pyrites
Many do not develop perfect geometric forms, but may do develop a characteristic shape that we can use for identification, some grow equally in all 3D, others are elongate in one direction or flattened if growth in one direction is surpressed.
Commonly used terms include equant (equidimensional) bladed A – flattened in one direction, fibrous, tabular, prismatic B - faces that are parallel to a common direction, banded – C stripes of bands of different colours and textures, platy, blocky and botryoidal D – intergrown crystals representing a bunch of grapes,

10. 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
Brittle Tenacity – describes a minerals toughness or resistance to breaking or deforming.

11. Mohs Mineral Hardness Scale
1) Talc
2) Gypsum
3) Calcite
4) Fluorite
5) Apatite
6) Feldspar
7) Quartz
8) Topaz
9) Corundum
10) Diamond
Softest 1 2 3 4 5 6 7 8 9 10
All minerals are compared to a standard scale called the Mohs scale of hardness which measures resistance to abrasion or scratching. Goes from soft to hard.
All minerals are compared to a standard scale called the Mohs scale of hardness
Hardest

12. 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
As we saw when briefly looking at the mineral structures, many have a structure or lattice that is not the same in every direction, and therefore have bonds that vary in strength.
As a result these minerals will fail or break with preference along these weaker bonds, these broken fragments are bounded by more or less flat PLANAR surfaces , and this is known as CLEAVAGE
Cleavage can be recognised by rotating a sample and looking for smooth, even surfaces that reflect light like a mirror.
However cleavage surfaces can occur in small flat segments arranged in stair-step fashion
The simplest form of cleavage is exhibited by micas, because they have such a weak bond in one direction than others

13. 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
Not all cleavage is as simple as micas, there are many forms,
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
Fluorite, halite, and calcite all exhibit perfect cleavage

14. Fracture & Density Fracture Density 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 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
When a mineral has structures that are equally or nearly equal in all directions, when we apply pressure they FRACTURE. The fracture pattern varies, such a quartz fractures into a conchoidal pattern, others into splinters or fibrous but most just fracture into irregular fragments
Density of a mineral is expressed as mass per unit volume. Often as grams per cubic cm
We use a related measure called Specific gravity to describe the density of minerals.
Specific gravity is a unitless number representing the ratio of a minerals weight to the weight of an equal volume of water.
Most common minerals have a SG of between 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.
This can be used to develop a rule of thump, if you have a mineral in your hand, compare it to rocks of a similar size you have handled and then the SG is about 2.5-3, if not it has a different SG

15. Physical properties of minerals
Magnetism
Reaction to hydrochloric acid - Effervesce
Malleability
Double refraction
Taste
Smell
Elasticity
In addition to these there are a number of additional secondary techniques
READ SLIDE
Lick halite
Talc feels soapy whilst graphite feels greasy
Sulfur smells like rotten eggs
Transparent calcite has an optical property of double refraction
Drop HCL on to carbon ates and it will EFFERVESCE - fizz

16. Structure of minerals Nicolas Steno (1638-1676)
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
The unit cells of halite join together in a regular manner creating the whole crystal. The shape and symmetry of the entire crystal relate to the shape and symmetry of the whole crystal.
However, it is rare to find perfect crystals in nature, but the angles between the equivalent crystal faces of the same mineral are remarkably consistent.
This observation was first made by Nicolas Steno in He found that the angle between adjacent prism faces of quartz crystals are 120 degrees regardless of sample size or provenance of the crystal. This observation is known as Law of Constancy of Interfacial Angles .
Because it applies to all minerals it states that “angles between equivalent faces of crystals of the same mineral are always the same” Therefore crystal shape is often a valuable tool in mineral identification.
HOWEVER, minerals can be built of geometrically similar building blocks yet exhibit different external forms. – Fluorite, magnetite and garnet are call constructed by cubic unit cells, yet they exhibit different shapes, and because the building blocks are so small they reslut in smooth flat surfaces.