Elements, minerals and rocks Flashcards
What is an element?
A substance made entirely of one type of atom.
How can Earth’s elements be classified?
The Goldschmidt system.
Define the atomphiles and give some examples.
Gas loving elements, which occur as liquids/gases at temperatures/pressures found on/above the Earth’s surface. Examples may include nitrogen, hydrogen and carbon.
Define the lithophiles and give some examples.
Rock loving elements which combine with oxygen to form low-density compounds which remain near Earth’s surface and are concentrated in the crust. Examples may include oxygen, silicon and sodium.
In the lithophiles what are the eight elements in this group and how much do they account for the weight of the Earth’s crust. (Same for silicate minerals)
-Oxygen (47%)
-Silicon (28%)
-Aluminium (8%)
-Iron (5%)
-Calcium (3.5%)
-Sodium (3%)
-Potassium (2.5%)
-Magnesium (2%)
Silicon and oxygen combine together and also with other elements to form what?
The Silicate minerals.
Define the chalcophiles and give some examples.
Ore-loving elements combine with sulphur to form higher density sulphides. They occur deeper than lithophiles and are concentrated in the mantle. Examples may include copper, lead and sulphur.
Define the siderophiles and give some examples.
Iron-loving elements that have a high density and combine more easily with iron than oxygen, forming dense compounds that occur in the Earth’s core. Examples may include iron, iridium and nickel.
What can the bulk composition of the Earth be postulated from?
Meteorites.
What are the types of meteorite and what are their compositions?
-Iron meteorites=composed of iron and nickel.
-Stony meteorites=composed of silicate minerals and are non-metallic.
What is undifferentiated?
Smaller bodies cooled and solidified too quickly for differentiation to take place, so these primitive meteorites are our best picture of the early history of the solar system since they have fewer influences for change over the age of the solar system.
What is differentiation?
As a larger body cools, more dense materials such as iron sink towards the centre.
What are undifferentiated stony meteorites also known as?
Chondrites.
What is a mineral?
A solid, inorganic and naturally occurring chemical compound/element with a defined structure and composition.
What are the distinct characteristics of minerals?
-Chemical compositions
-Atomic structures
-Physical properties by which they may be identified
What are the two main element groups?
The two main element groups are the major elements and the minor elements.
What is the main process that forms minerals?
Crystallisation
What happens when water is 0 degrees celcius?
The temperature decreases, so crystals of ice start formation.
What happens when magma starts to cool and then when it cools below its melting point?
Solid minerals crystallise. When magma cools below its melting point, crystals of minerals begin to form.
When can this process occur and what happens if this continues?
When liquids evaporate from a solution. When water evaporates, the concentration of salt is a lot higher, so the solution becomes saturated. If continual evaporation occurs, salt will precipitate/drop out of solution a crystals.
What are the main physical properties of minerals?
-Hardness
-Density
-Cleavage/fracture
-Streak
-Lustre
-Colour
-Other diagnostic properties (crystal shape, reaction with HCl acid and twinning)
What is hardness and how can it be tested?
Hardness is the resistance of a mineral to scratching. It can be tested by Moh’s scale which chooses ten common reference minerals. Fingernails (2.5), copper coins (3.5), steel blade (5.5) and glass (7).
What is density and how can it be tested?
Density is the mass per volume and is dependant on chemical composition and crystal habit. Density can be calculated by mass/volume or displacement of water. Hefting can also be used to approximate which mineral is denser.
What is colour?
Reflects the chemical composition of a mineral. Felsic=light mineral and mafic=dark mineral.