1.1 Minerals and mineral properties Flashcards
How are minerals formed? 1-5
Solidification from a melt ( igneous minerals) Hydrothermal fluids Recrystallisation during metamorphism Evaporation of solutions Cement precipitated from pore waters
Explain solidification from a melt?
When molten rock cools crystals form creating igneous rocks
Magma cools slowly to form large crystals
Cools quickly to form small crystals
Minerals from melt crystallisation - quartz, feldspar, mica, olivine,augite
Explain hydrothermal fluids?
Hot water deep in earth dissolves minerals out of rocks
Fluids rise - temperature and pressure reduce
Minerals precipitated as euhydral crystals
Minerals from hydrothermal fluids appear in veins and faults
Gangue minerals - quartz and calcite
Ore minerals- haematite and galena
Explain recrystallisation during metamorphism?
Increased pressure and/or temperature can cause minerals to fall out of equilibrium with the surroundings
They recrystallise into a more stable form
Minerals - calcite and garnet
Explain evaporation of solutions?
Seawater has 3.5% dissolved minerals
When water evaporates a range of materials are precipitated
See diagram
Eg first calcite then gypsum and then halite
Explain cement precipitated from pore waters?
Pore is a small hole between grains in a sedimentary rock
Pore fluids rise through sediments changes in temperature and pressure causes minerals to precipitate as cement sticking grains together
Quartz and calcite
What is a diagnostic property?
It allows a mineral to be identified
Minerals have distinctive properties based on chemical composition and atomic structure
These properties distinguish between minerals
What are gangue minerals?
Waste minerals that have useful minerals inside them
Eg quartz and calcite
What are ore minerals?
Minerals containing valuable metal eg haematite and galena
What are semi precious stones?
Minerals which are rare and valued for their appearance
How are hydrothermal veins formed?
Faults provide a space in rock
Hot fluids from magma rise through the vein
Crystallise as they cool due to geothermal gradient
What are minerals?
A naturally occurring inorganic substance that has a specific chemical composition and characteristic atomic structure
Or
A solid chemical element or compound found naturally
How do we identify mineral properties? 1-9
Colour - not diagnostic Lustre Streak Relative density Hardness Fracture Cleavage Reaction with HCL Taste
What do we learn from colour?
It is not a diagnostic property Use - appearance of mineral under white light Observe minerals in white light Eg pyrite is brassy yellow Quartz is colourless
How do we use lustre?
The way in which a mineral reflects white light
Tilt the mineral back and forth to reflect the light
Eg quartz is vitreous
Galena is metallic
Muscovite is pearly
