Characterisation Of Minerals Flashcards
Characterisation of minerals is done by which criterion?
Colour
Lustre
Form(shape,group,clustering)
Hardness(resistance to abrasion)
Cleavage(preferential split, only minerals have this, rocks have planar weaknesses)
Fracture(nature of broken surface)
Tenacity(malleable or brittle)
Specific gravity
What are the two main mineral classes?
Silicate (65%)
oxygen and silicon are chief rock forming minerals
Non-silicate(35%)
Carbonates,oxides,halides,sulphides,sulphates,phosphorites
The mica group belongs to which mineral type?
Silicate
Describe the mica group
Easily split into thin flakes due to perfect cleavage parallel to basal plane
Two types of mica?
Mascovite- colourless,silvery
Biotite-dark brown/black
Describe the feldspar group
Very common minerals found in the earth’s crust
2 types of feldspar?
Alkali feldspar
Plagioclase feldspar
The feldspar group also belongs to which mineral group?
Silicate
What are the six main silicate minerals?
Olivine
Pyroxene
Amphibole
Mica
Feldspar
Silica
Of the silicate minerals, which is the most susceptible to weathering?
In order: olivine, pyroxene, amphibole, Mica, Feldspar and Silica
How does Mica weather?
Complex reaction where metal ions are removed from mineral.
Reaction results in soluble ions and clay minerals.
How does Feldspar weather?
They weather via hydrolysis
As water is absorbed into the feldspar, kaolinite is often formed
The S in feldspar stands for hydrolysis
What is a dyke?
A sheet of rock formed in a fracture of a pre-existing rock through the rising of magma
What is a sill?
A sheet intrusion that has intruded between older layers of sedimentary rock or lava
What is the difference between intrusive and extrusive igneous rock?
Extrusive cools quickly above ground
Intrusive rocks cool quickly beneath ground
The silica content in rock varies from []-[]% ?
40-80%
High silica rocks are [ ]
Felsic or acidic (silic-felsic)
Low silica rocks/ metallic oxides are [ ]
Mafic/basic (mafICK, metallICK)
What is the significance of an igneous rock being intrusive or extrusive?
Extrusive cools quickly, finer grains(no colour separation)
Intrusive cools slowly, larger grains
What does it mean if your igneous rock has large minerals?
It had plenty of time to cool (intrusive)
What are the two types of eruptions?
Fissure and central
What is special about a fissure eruption?
They occur when a dike penetrates the surface.
Low viscosity flow, goes far (runny)
Fine grained Basaltic lava (fine balls)
What is special about central eruptions? (Explosive, command centre go BOOM)
Ejection of lava, ashes and gas
What is meant by pyroclastic?
Produced by volcanic ejections
Pyro - crazy
Clastic -fantastic!boom!
Crazy boom rock
Igneous rocks can range from [] to []
Felsic to ultramafic
The more mafic, the more []
Reactive
Mafic-mafia-excitable
A more mafic igneous rock sits higher or lower in the silicate mineral reactivity scale?
Higher
Mafic -less silica content- more reactive
What is meant by equigranular texture?
All crystals are of approximately the same size
What is meant by inequigranular?
Some crystals are larger than others
What is meant when a rock is porphyritic?
Large crystals surrounded by smaller ones
Porphyritic - poor - parasitic
Little ones flock to the big one
What is meant by a Phaneritic rock texture?
A rock with large, clearly visible interlocking crystals
I’m a BIG “phan”
What is meant by an aphantic rock texture?
Aphantic frantic hard to find
Too fine grained for mineral constituents to be identified
What is significant about euhedral minerals in a rock?
Clearly defined edges, formed first and so got to have a defined shape
What is significant about anhedral minerals in a rock?
Formed after the euhedral minerals
Have less defined edges
