Minerals Pt.2 (L5) Flashcards
The appearance and physical behaviour of minerals are directly related to _______
their chemical composition and bonding characteristics of their components (informative
Do all minerals have the same exact set of properties? Y or N
No
What is crystal habit?
refers to the external geometric shape of mineral crystals
What is cleavage?
It is used for mineral identification
it is the breakage of a mineral along flat, well-defined planes. Occurs in minerals that have bonds of diff strengths
What does cleavage refer to?
refers to how a mineral crystal breaks, NOT its external crystal form
Cleavage is a manifestation of the internal structure of mineral crystals
What is the simplest case of cleavage? And what can it be used for?
Mica - breaks in one direction
breaks into tiny little flakes that reflect light very well so commonly used as cosmetic glitter
Which way will cleavage break?
in the direction of weaker bonding
may be more than one direction of weaker bonding
Basal Cleavage
Cleavage in one direction
Cubic Cleavage
3 directions at 90 degrees
rhombohedral cleaveage
3 directions not at 90 degrees
Octahedral cleavage
four directions at 90 degrees to form a 3d shape with 8 sides
Why are cleavage planes always surfaces of breakage and don’t follow the same direction as the crystal faces?
Because cleavage is an internal property (breakage along planes of weakness) while the crystal faces is an external property
Why do not all minerals show cleavage?
b/c in some minerals, the bonds are relatively uniform in strength, so don’t break along specific planes
Fracture
The appearance of a broken surface that isn’t cleavage
what is the easiest type of fracture to recognize?
Conchoidal fracture
named b/c of the arc-shaped patterns on the surface that resemble the inside of a seashell
Hardness
Another useful diagnostic property
measure of the resistance of minerals to abrasion or scratching
what does the hardness of a mineral reflect?
the overall strength of bonding within its crystal structure
stronger bond = greater hardness
How is hardness measured
Mohs scale of hardness
How do you use Moh’s original hardness scale
we can test it against minerals or other objects of known hardness
Higher hardness will scratch mineral with lower hardness
What is Specific Gravity
a number representing the ratio of the weight of a mineral to the weight of an equal volume of water
or we can just say that some minerals are heavier than others
Diaphaneity
the ability of a mineral to transmit light
3 types the Diaphaneity
transparent, translucent, or opaque
Transparent Minerals
transmit light in an undisturbed fashion, like clear glass
Transculent Minerals
the light entering the mineral is scattered as it is transmitted (can’t see the details of whatever is on the other side)
Opaque
it means that no light is transmitted through the material
Why is transclucency tricky to recognize?
b/c it is between transparency and opaque
Lustre
the ability of a mineral to reflect light from its surface
how is Lustre diff from diaphaneity?
Lustre doesn’t deal with the transmission of light but more on the surface reflection
Lustre can be either __ or __
metallic or nonmetallic
Colour
manifests the chemical content of a mineral
color can be a very diagnostic property
Why can colour sometimes be misleading? Example?
minor impurities or crystal defects can impart strikingly diff colors
Tourmaline (ex): depending on the metals present in this mineral, the color can vary significantly, sometimes even within the same crystal
Powder
Another way of identifying some minerals
we do this by rubbing the mineral specimen against an unglazed porcelain plate called a streak plate
the streak of hematite is always a ____ colour
reddish brown
magnetism
very diagnostic, although limited to only a few minerals
If a mineral fizzes which mineral is it most likely to be?
Limestone (used in TUMS)
Strange optical properties
some minerals will produce a double image when an object is viewed through its crystals
Birefringence
due to the splitting of light rays as they pass through the calcite crystal
Most minerals can be identified on the basis of __?
a unique combination of physical properties
Sphalerite (ZnS) unique property?
smell of rotten eggs when rubbed
Unique property of Graphite?
greasy lustre, is opaque, very soft
Unique property of Halite?
tastes salty
Unique property of Talc?
Slippery or soapy (used in baby powder)
