Mineral introduction
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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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Mineral Introduction

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Mineral introduction

Mineral Introduction


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


    Mineral introduction

    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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