Mineral Introduction. Minerals: Building blocks of rocks By definition a mineral is Naturally...
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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
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
Slide 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 On this basis, ice is indeed
a mineral: it is of hexagonal structure, of fundamental composition
H 2 O, transparent and colourless, with Mohs hardness 1.5 and
calculated specific gravity 0.917.
Slide 4
Classification of Mineral groups Nearly 4000 minerals have been
named Rock-forming minerals Common minerals that make up most of
the rocks of Earths crust Only a few dozen members Composed mainly
of the 8 elements that make up > 98% of the continental
crust
Slide 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
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
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
Slide 7
Colour Generally unreliable for mineral identification Often
highly variable due to slight changes in mineral chemistry Exotic
colorations of certain minerals produce gemstones Quartz (SiO 2 )
exhibits a variety of colours Multicoloured tourmaline
Slide 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
Slide 9
Habit crystal shape 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 Refers to the common characteristics of shape of a crystal
or an aggregate of crystals
Slide 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
Slide 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 Hardest 1 2 3 4 5 6 7 8 9 10 All minerals are
compared to a standard scale called the Mohs scale of hardness
Slide 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
Slide 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 Fluorite, halite, and
calcite all exhibit perfect cleavage
Slide 14
Fracture & Density Fracture Absence of cleavage when a
mineral is broken Quartz fractures into a conchoidal pattern
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.
Slide 15
Physical properties of minerals Magnetism Reaction to
hydrochloric acid - Effervesce Malleability Double refraction Taste
Smell Elasticity
Slide 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