Igneous rocks are formed when magma cools. If it solidifies underground the resulting rocks are said to be plutonic. If the molten magma is emitted by a volcano, and subsequently solidifies, the rocks are volcanic.
When molten magma cools, minerals crystallise out in order of their melting
points, highest first, as given by Bowen's Reaction Series, which has two branches.
If the magma is rich in iron and magnesium, but poor in silicon, then the order is
olivine, then
pyroxene,
amphibole and
biotite; this is the discontinuous
branch. If the magma is rich in silicon but poor in iron and magnesium then there is a
continuous series from calcium-rich plagioclase feldspar,
anorthite,
to sodium-rich plagioclase feldspar,
albite (variety oligoclase). Thereafter
the two branches combine, and orthoclase (K-spar)
crystallises, followed by muscovite
and finally quartz. These are the major rock-
forming minerals, although other minerals may be present as minor constituents.
Volcanic rocks develop when molten magma solidifies at the Earth's surface after eruption from a volcano. The chemical composition and mineral constitution of volcanic rocks are similar to those of the corresponding plutonic rocks.
Pegmatites are particularly large-grained rocks that are formed in the final phase of
crystallisation of plutonic rocks. Some portion of highly volatile components, especially
water, is left over, and it contains all the elements that are too large or too small to be
incorporated in the normal rock minerals (quartz,
feldspar and mica).
These are chiefly elements like lithium, beryllium, niobium, tantalum, cesium and rare earths.
Pegmatites can be of any plutonic rock type, but they are most commonly
granitic.
Essential constituents are
feldspar,
mica and
quartz.
Common but not essential constituents include
albite,
microcline,
muscovite,
topaz and
tourmaline.
In addition many rare minerals form exclusively or mainly in pegmatites.
Pegmatites may be simple or complex.
Simple pegmatites contain only the minerals quartz,
feldspar and mica.
Complex pegmatites result from the crystallisation of the last hydrous and gaseous portion of the magma, with its higher
concentration of rare elements, and so they contain a greater variety of minerals.
Most pegmatites have four zones:
1. The border zone is fine-grained, seldom thicker than 1 m, and usually consisting of
aplite.
2. The wall zone is coarser-grained and thicker than the border zone and surrounds the pegmatite body more or less
completely; it contains both common minerals and rarer minerals such as
apatite,
columbite-tantalite,
garnet and beryl.
3. The intermediate zone may be absent in some pegmatites. Where it occurs it is very coarse-grained and may contain
giant crystals of spodumene,
amblygonite and perthite.
4. The core zone, if present, is irregular in shape and consists of quartz,
perthite, spodumene and
amblygonite
(AS).
Pegmatites may be described in terms of the rare elements that they contain.
NYF pegmatites contain niobium Nb, yttrium Y and fluorine F; they are derived from extensional tectonic events
(R&M 97.3.211)
LCT pegmatites are derived from collisional tectonic events (R&M 97.3.211); they contain lithium Li, cesium Cs and
tantalum Ta; they are much more abundant than NYF pegmatites, and, in
addition to Li, Cs and Ta, they tend to be enriched in beryllium Be, boron B, fluorine F, phosphorus P,
manganese Mn, gallium Ga, rubidium Rb, niobium Nb, tin Sn and hafnium Hf. They are also peraluminous, ie
molecular Al/(Na + K + 2Ca) > 1. Peraluminous pegmatites have an abundance of
muscovite or lepidolite, and are
likely to contain tourmaline and garnet,
and, more rarely, gahnite, topaz or
andalusite
(R&M 92.2.144-155).
The elbaite subtype designates pegmatites in which most of the
lithium is stored in tourmaline
(Mineralogy and Petrology 55.159-176).
Pegmatites also may be classified according to geological location, leading to division of granitic pegmatites into five
classes, abyssal, muscovite, muscovite–rare element, rare element, and miarolitic, most of which are further subdivided
into subclasses,
Abyssal Class (AB)
Metamorphic Environment: ~4 to 9 kbar, ~700 to 800oC,
granulite facies
Muscovite Class (MS)
Metamorphic Environment: 5 to 8 kbar, ~650 to 580oC,
amphibolite facies
Muscovite-Rare Element Class (MSREL)
Metamorphic Environment: 3 to 7 kbar, ~650 to 520oC,
greenschist to
amphibolite facies
Rare Element Class (REL)
Metamorphic Environment: ~2 to 4 kbar, ~650 to 450oC, low pressure
greenschist to
amphibolite facies
Miarolitic Class (MI)
Metamorphic Environment: 3 to 1.5 kbar, 500 to 400oC, very low pressure
greenschist facies
(CM 43.6.2005-2026).
Carbonatites are igneous rocks that consist largely of the carbonate minerals
calcite and
dolomite; they sometimes also contain the rare-earth ore minerals
parisite, and
monazite, and the niobium ore mineral
pyrochlore. The origin of carbonatite
magma is
obscure. Most carbonatites occur close to intrusions of
mafic igneous rocks or to
ultramafic igneous rocks such as
kimberlite. Carbonatites occur in small plutonic bodies.
Carbonate minerals make up at least 50% of carbonatites.
Essential constituents are
calcite and
dolomite.
Common but not essential constituents include
ankerite and
siderite.
Natrocarbonatite is a carbonatite composed essentially of sodium +/-potassium +/-calcium carbonate minerals and
gregoryite and nyerereite are
essential constituents. Currently (June 2022) a lava is known from only one locality,
Ol Doinyo Lengai, Ngorongoro District, Tanzania (Mindat).
Calcite-carbonatite is a carbonatite where more than 90% of the carbonate is
calcite (Mindat).
Clastic sedimentary rocks form from at the earth's surface by oxidation, weathering, erosion and deposition. When granitic rocks weather at the earth's surface feldspar alters into clay minerals, particularly kaolinite, sometimes forming large deposits. Most sedimentary rocks are initially deposited as unconsolidated sediments. Consolidation sets in only gradually because of dewatering and/or because of the cementation with a binding material (clayey, calcareous or siliceous). Clastic sedimentary rocks are classified largely by grain size.
Chemical sediments are created either by the deposition of insoluble precipitates, or by the evaporation of sea water
or saline lakes in arid regions. The latter are called evaporite deposits. Typical evaporite minerals are
halite,
borax, colemanite and
ulexite.
A salt dome is a type of structural dome formed when a thick bed of evaporite minerals, mainly
halite, occurring at depth intrudes vertically into surrounding rock strata.
Biogenic sedimentary rocks form from remains of living creatures. Some rocks, such as chert, may form both as biogenic deposits and as chemical deposits.
Placer deposits are accumulations of heavy and corrosion-resistant minerals in rivers and
lakes. The minerals are formed elsewhere, and carried down by currents of water. Typical
placer minerals are gold,
platinum,
garnet,
ilmenite,
rutile, and
monazite.
A gem gravel is a gravel placer containing an appreciable concentration of gem minerals.
Changes which occur in solid rock in response to changes in pressure and temperature are categorised as diagenetic
or metamorphic. There is no clear boundary between these two types of change. Processes at pressures below about
1 kbar and temperatures below about 100oC are usually categorised as diagenetic. These include changes
which form sedimentary rocks from chemical
or clastic sediments.
Processes at higher pressures and temperatures are usually
categorised as metamorphic, and these processes proceed more quickly in the presence of circulating
hydrothermal fluids, which may originate from an intruding magma, from regional metamorphic reactions, or
from surface water.
Both igneous and sedimentary rocks are subject to metamorphism at sufficient temperature and pressure, and the
resulting minerals are largely determined by the composition of the original, unaltered rock, called the protolith.
Metamorphism can involve recrystallisation of existing minerals, the formation of new minerals through chemical
reactions, and the transformation of a mineral from one paramorph to another.
Typical metamorphic minerals include andalusite,
garnet, kyanite,
magnetite and
pyrrhotite.
Contact metamorphism results from high temperatures usually due to the proximity to a body of magma.
Regional metamorphism is due to pressure and temperature changes over large areas during
mountain building and subduction.
Certain minerals known as index minerals first appear at different temperatures; with increasing temperature these
minerals are
chlorite,
biotite,
garnet,
staurolite,
kyanite, and
sillimanite.
The index minerals generally persist into
higher grade zones (higher temperature), and may survive
progressive metamorphism and be present with other index minerals, for example,
chlorite can frequently be found in
biotite
schist and garnet is often present in
kyanite schist.
cordierite also frequently occurs in place of
garnet.
Metasomatic metamorphism is the action of hydrothermal fluids from a metamorphic source, causing chemical alteration of a rock. It is the replacement of one rock by another of different chemical composition. The minerals which compose the rocks are dissolved and new minerals are deposited in their place. Dissolution and deposition occur simultaneously and the rock remains solid (Wiki)
New minerals are often formed when the metamorphic grade increases (temperature and/or pressure increase); this is termed prograde metamorphism. If the metamorphic grade decreases (temperature and/or pressure decrease) and new minerals are formed this is termed retrograde metamorphism.
Different minerals form from metamorphism at different temperatures and pressures. Low temperature and pressure
is designated as low-grade metamorphism, and high temperature and pressure as high-grade metamorphism. The
various ranges of conditions are called metamorphic facies, often named for the dominant mineral found there. The boundaries
of the different facies are not sharp, and there is appreciable overlap. Different sources give different values for the
boundaries. The ones listed below are in fairly common usage.
The major facies, in order of increasing temperature within pressure band, are
Low Pressure
Medium Pressure
High Pressure
In the greenschist, amphibilite and granulite facies, with increasing temperature minerals firt appear in the order chlorite, biotite, garnet, staurolite, kyanite and sillimanite.
The zeolite facies is a low-grade metamorphic facies resulting from burial in thick sedimentary basins at temperature
50 to 270oC and pressure 0.3 to 5 kbar.
Zeolites are characteristic minerals.
Changes in mineralogy are most prominant in clay-rich, fine-grained
clastic sediments (pelitic sediments), with transformation of clay minerals to
muscovite variety illite,
kaolinite and
vermiculite.
Typical assemblages include:
Kaolinite and
montmorillonite with
laumontite,
wairakite,
prehnite,
calcite and
chlorite,
and, in potassium-rich rocks,
muscovite variety illite and
orthoclase variety adularia.
Generally plutonic and volcanic rocks are not affected by zeolite facies metamorphism,
although vesicular basalt frequently has its vesicles filled with
zeolite minerals.
This is a low-grade metamorphic facies associated with
contact metamorphism at temperature 250 to 500oC and pressure less
than 2 kbar.
It often
forms the outer portions of a thermal aureole (a region in country rock around an igneous intrusion that has
experienced metamorphism due to heat from the body of magma).
Albite and epidote are characteristic
minerals and hornfels is a characteristic rock.
Typical assemblages include:
Mafic protolith:
actinolite,
epidote,
chlorite,
biotite,
talc and
albite.
Pelitic (clay-rich, fine-grained clastic sedimentary) protolith:
quartz,
albite,
epidote,
chlorite,
muscovite,
biotite and
andalusite.
Quartzofeldspathic (rich in quartz and
feldspar) protolith:
microcline,
albite,
quartz,
biotite and
muscovite.
Calc-silicate protolith (calcitic and dolomitic limestones):
calcite,
epidote and
tremolite.
This is a medium-grade metamorphic facies associated with contact metamorphism
at temperature 450 to 650oC
and pressure less than 2.5 kbar.
The absence of epidote, chlorite and
albite distinguishes rocks of this facies from those of the
albite-epidote-hornfels facies.
Hornblende is a characteristic mineral and
hornfels is a characteristic rock.
Typical assemblages include:
Mafic protolith:
hornblende,
tremolite,
plagioclase feldspar,
biotite,
cordierite,
anthophyllite,
quartz and
almandine.
Pelitic (clay-rich, fine-grained clastic sedimentary) protolith:
hornblende,
tremolite,
quartz,
plagioclase feldspar,
muscovite,
biotite,
andalusite and
cordierite.
the presence of
hornblende, and of muscovite
in this assemblage
distinguishes it from the pyroxene-hornfels facies.
Biotite,
cordierite
and andalusite can occur as porphyroblasts (large crystals in a
finer groundmass in a rock produced by metamorphic recrystallisation), often rich in inclusions,
but these
minerals are not restricted to this facies.
Quartzofeldspathic (rich in quartz and
feldspar) protolith:
microcline,
quartz,
biotite,
muscovite and
almandine.
Calc-silicate protolith (calcitic and dolomitic limestones):
calcite,
plagioclase feldspar,
tremolite,
grossular,
diopside and
quartz.
This is a high-grade metamorphic facies associated with contact metamorphism
at temperature 650 to 800oC
and pressure less than 2.5 kbar.
Rocks of
this facies often form the innermost zone of a thermal aureole (a region in country rock around an igneous intrusion
that has
experienced metamorphism due to heat from the body of magma).
Pyroxenes are characteristic minerals and
hornfels is a characteristic rock.
Typical assemblages include:
Mafic protolith:
plagioclase feldspar,
biotite,
cordierite,
orthopyroxene,
quartz and
diopside.
Pelitic (clay-rich, fine-grained clastic sedimentary) protolith:
quartz,
plagioclase feldspar,
microcline,
andalusite or
sillimanite and
cordierite.
The absence of muscovite and
hornblende and the presence of
pyroxene in mafic rocks and
sometimes in
pelitic rocks distinguishes these assemblages from the
hornblende-hornfels facies. In pelitic rocks
biotite,
cordierite and andalusite or
sillimanite can occur as porphyroblasts (large crystals in a
finer groundmass in a rock produced by metamorphic recrystallisation), often rich in
inclusions.
Quartzofeldspathic (rich in quartz and
feldspar) protolith:
microcline,
quartz,
biotite and
plagioclase feldspar.
Calc-silicate protolith (calcitic and dolomitic limestones):
calcite,
plagioclase feldspar,
grossular,
diopside,
quartz and
wollastonite.
This is a high-grade metamorphic facies associated with contact metamorphism
at a temperature in excess of
800oC and pressure less than 2.5 kbar.
Rocks of
this facies are relatively rare and sometimes form the innermost zone of
thermal aureoles (regions in country rock around an igneous intrusion that has
experienced metamorphism due to heat from the body of magma) or more commonly as partially resorbed xenoliths
within magmas.
Sanidine is a characteristic mineral, and hydrous minerals such as
biotite are absent.
The spurrite-merwinite facies is a subfacies of the sanidinite facies.
This is a low-grade metamorphic facies typically resulting from subseafloor alteration at mid-ocean
ridges, or from burial in thick sedimentary basins at temperature 250 to 350oC and pressure 2 to 6 kbar.
A mid-ocean ridge is an underwater mountain range, formed at the boundary of two tectonic plates that are moving apart,
so that magma wells up between them, forming the ridge.
Prehnite and
pumpellyite are characteristic minerals and
slate is a characteristic rock.
Typical assemblages include:
Mafic protolith:
prehnite,
pumpellyite,
chlorite,
albite and
epidote;
actinolite occurs at higher temperature and
lawsonite at higher pressure.
Pelitic (clay-rich, fine-grained clastic sedimentary) protolith:
muscovite variety illite,
chlorite,
albite
and stilpnomelane.
Quartzofeldspathic (rich in quartz and
feldspar) protolith:
albite,
chlorite,
pumpellyite,
prehnite,
stilpnomelane,
muscovite,
titanite,
epidote and carbonate;
actinolite replaces
prehnite at higher temperature;
lawsonite occurs at higher pressure.
Calc-silicate protolith (calcitic and dolomitic limestones):
calcite,
dolomite,
prehnite,
albite,
chlorite and
quartz.
This is a low-grade metamorphic facies associated with regional metamorphism
at temperature 350 to 500oC
and pressure 1 to 10 kbar.
Chlorite and biotite
are characteristic greenschist facies minerals, and
epidote is also common, but is not restricted to this facies.
Slate,
phyllite and schist
are characteristic greenschist facies rocks.
Typical assemblages include:
Mafic protolith:
albite,
chlorite,
actinolite,
epidote,
titanite,
quartz,
muscovite and
calcite;
stilpnomelane
occurs at low temperature and biotite and
hornblende occur at higher temperature.
Pelitic (clay-rich, fine-grained clastic sedimentary) protolith:
muscovite,
chlorite,
albite,
paragonite,
graphite,
rutile, carbonate,
epidote,
K-feldspar,
titanite,
stilpnomelane (low aluminium protoliths),
pyrophyllite (high aluminium protoliths) and
chloritoid (high-Al protoliths);
biotite occurs at higher temperature;
garnet occurs at the highest temperatures.
Quartzofeldspathic (rich in quartz and
feldspar) protolith:
albite,
epidote,
muscovite,
chlorite,
titanite,
stilpnomelane,
actinolite;
biotite
and garnet occur at higher temperatures.
Calc-silicate protolith (calcitic and dolomitic limestones):
calcite,
dolomite,
graphite,
quartz,
muscovite,
albite,
K-feldspar,
chlorite and
zoisite.
This is a medium grade metamorphic facies associated with regional metamorphism
at temperature 500 to
800oC and pressure 2 to 14 kbar.
Garnet, staurolite,
kyanite, hornblende and
sillimanite
are characteristic amphibolite facies minerals.
Amphibolite is the characteristic amphibolite facies rock, and
schist and gneiss are also amphibolite
facies rocks.
Typical assemblages include:
Mafic protolith:
hornblende,
oligoclase,
epidote,
almandine,
titanite,
quartz,
chlorite and
biotite.
Pelitic (clay-rich, fine-grained clastic sedimentary) protolith:
biotite,
muscovite,
oligoclase,
almandine,
cordierite (low pressure),
andalusite (low pressure),
kyanite (high pressure),
sillimanite (moderate pressure and/or high temperature),
staurolite (high temperature),
graphite and
titanite.
Quartzofeldspathic (rich in quartz and
feldspar) protolith:
oligoclase,
K-feldspar,
muscovite,
biotite and
hornblende.
Calc-silicate (calcitic and dolomitic limestones) protolith:
calcite,
dolomite,
quartz,
diopside,
tremolite,
forsterite,
graphite,
grossular,
hornblende and
clinozoisite.
Rocks of the amphibolite facies can undergo partial melting at 650 to 700oC in the presence of water
resulting from dehydration reactions.
This is a high grade metamorphic facies associated with
regional metamorphism at temperature above 700oC
and pressure above 2 kbar.
Kyanite and sillimanite
are characteristic granulite facies minerals.
Granulite and gneiss
are characteristic granulite facies rocks.
Amphibole and mica are both absent in
granulite facies rocks, and hornblende
dehydrates to form pyroxene and
plagioclase feldspar. Kyanite and
sillimanite are often produced
from muscovite and biotite.
Typical assemblages include:
Mafic protolith:
plagioclase feldspar,
pyroxene,
hornblende,
olivine (low pressure),
garnet and
quartz.
Pelitic (clay-rich, fine-grained clastic sedimentary) protolith:
microcline,
plagioclase feldspar,
scapolite,
garnet,
cordierite (low pressure),
andalusite (low pressure),
kyanite (high pressure),
sillimanite (moderate to low pressure, high temperature),
graphite,
rutile,
ilmenite,
olivine,
corundum,
spinel and
sapphirine (high temperature).
Quartzofeldspathic (rich in quartz and
feldspar) protolith:
microcline,
plagioclase feldspar,
garnet,
pyroxene and
hornblende.
Calc-silicate protolith (calcitic and dolomitic limestones):
calcite,
dolomite,
quartz,
diopside,
scapolite,
forsterite,
wollastonite and
graphite.
This is a low to medium grade metamorphic facies associated with subduction at temperature 100 to 500oC
and pressure greater than 4 kbar.
Glaucophane and jadeite
are characteristic blueschist minerals, and chlorite,
epidote and
kyanite are
common.
Slate and schist are
characteristic blueschist facies rocks.
Typical assemblages include:
Mafic protolith:
glaucophane,
lawsonite,
jadeite (high pressure),
actinolite or
hornblende,
albite (low pressure),
titanite,
pumpellyite,
stilpnomelane,
epidote and
garnet.
Pelitic protolith:
glaucophane,
chlorite,
muscovite,
paragonite,
lawsonite,
epidote,
kyanite,
quartz
(or coesite at very high pressure),
chloritoid and
titanite.
Quartzofeldspathic (rich in quartz and
feldspar) protolith:
jadeite (high pressure),
lawsonite,
muscovite,
chlorite,
titanite and
glaucophane.
Calc-silicate protolith:
calcite and
aragonite.
This is a high-grade metamorphic facies associated with subduction at temperature in excess of 250oC and
pressure greater than 12 kbar.
Omphacite and pyrope are
characteristic eclogite facies minerals.
Eclogite facies rocks also occur as mantle xenoliths within mantle derived magma such as
kimberlite.
At very high pressures eclogite
facies rocks contain coesite, the high pressure
paramorph of silica.
Typical assemblages include:
Mafic protolith:
omphacite (clinopyroxene),
pyrope-rich garnet,
kyanite,
rutile,
quartz (low pressure) and
coesite (high pressure).
Pelitic (clay-rich, fine-grained clastic sedimentary) protolith:
omphacite-rich garnet,
carpholite,
muscovite,
chloritoid,
kyanite and
quartz, or
coesite at very high pressure.
Eclogite facies rocks often experience retrograde metamorphism (changes that occur during uplift and cooling of a
rock) during exhumation to
shallow depth.
Volcanic sublimates are minerals that form directly from volcanic gases during a discharge or eruption.
Some minerals form under the earth in geothermal wells, or in hot springs when the heated fluids rise to the surface.
Minerals that crystallise directly from volcanic gases and hot springs are
primary minerals.
Sulphur is typical of volcanic sublimates, and
realgar is a common mineral in hot spring deposits.
A fumarole is a vent in the surface of the Earth or another rocky planet from which hot volcanic gases and vapours are
emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcanic
activity, but fumarole activity can also precede a volcanic eruption and has been used for eruption prediction. Most
fumaroles die down within a few days or weeks of the end of an eruption, but a few are persistent, lasting for decades
or longer.
The predominant vapour emitted by fumaroles is steam, formed by the circulation of groundwater through heated rock.
This is typically accompanied by volcanic gases given off by magma cooling deep below the surface
(Wiki).
A coal-seam fire is a burning of an outcrop or underground coal-seam. Most coal-seam fires exhibit smouldering
combustion, particularly underground coal-seam fires, because of limited atmospheric oxygen availability. Coal-seam fire
instances on Earth date back several million years. Due to thermal insulation and the avoidance of rain/snow
extinguishment by the crust, underground coal-seam fires are the most persistent fires on Earth and can burn for
thousands of years. Coal-seam fires can be ignited by self-heating of low-temperature oxidation, lightning, wildfires and
even arson (Wiki).
The IMA allows products of combustion to be considered minerals as long as the fire was started naturally and no
anthropogenic materials were deposited in the mine
(AM 107.1982).
Hydrothermal replacement includes the process of one mineral replacing another, such as when silica replaces wood fibres in petrified wood, of one mineral forming a pseudomorphs of another, and of an ore body taking the place of an equal volume of rock. Replacement occurs when a mineralising solution dissolves the original mineral and almost simultaneously replaces it by another. Early-formed replacement minerals may themselves be replaced by later minerals. Replacement can occur in any type of rock, but especially in limestone, because of its easy solubility in acidic fluids.
The hydrothermal fluids circulating in hydrothermal veins are both water percolating
down from the surface, and volatile fluid rising up from the magma. The fluid is somewhat
acid, and dissolves some of the minerals in the wall rock at the top of the vein, leaving a
leached zone depleted of minerals. Further down, in the oxidation zone, a variety of
minerals, often sulphates, is deposited. These minerals are
secondary supergene minerals, derived from
the original primary minerals through chemical processes.
Still further down, just below the water table, there is a reducing environment, and the minerals in solution are
redeposited as secondary hypogene minerals, often sulphides.
This is the enriched zone, or zone of supergene
enrichment. Below this are unchanged,
primary minerals.
Hydrothermal veins may be low temperature (epithermal) (100oC to 200oC), medium temperature
(mesothermal) (200oC to 300oC)
or high temperature (hypothermal) (300oC to 500oC), and the suite of minerals found in each
type of vein is generally different.
Many hydrothermal minerals occur filling cavities in basalt. The cavities are formed by expansion of gas in volatile-bearing magmas at low pressures. The cavities may be filled by later minerals such as carbonates, quartz, zeolites, analcime or chlorite, formed by hydrothermal processes.
Cave deposits, are secondary mineral deposits formed in a cave, typically in limestone or dolostone solutional caves.
Guano deposits, are secondary mineral deposits generally formed in a cave. Guano is derived from the interaction of bat or bird urine and droppings, and limestone. It is rich in phosphate and nitrate, and a valuable fertiliser
The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust, at about 10 km under the oceans and about 35 km under the continents, and ends at the top of the lower mantle at 670 km. Temperatures range from approximately 227°C at the upper boundary with the crust to approximately 930°C at the boundary with the lower mantle. Upper mantle material that has come up onto the surface comprises about 55% olivine, 35% pyroxene, and 5 to 10% of calcium oxide and aluminum oxide minerals such as plagioclase, spinel or garnet, depending upon depth (Wiki).
Meteorites may be stony, stony-iron or iron meteorites.
Stony meteorites consist mostly of silicates. They are the most abundant kind, and may be chondrites or
achondrites.
Achondrites
were once molten, and chondrites were not. Chondrites are the most primitive meteorites in the solar system
(https://www.britannica.com/science/stony-meteorite).
Impacts on the parent body of a meteoroid can produce very large pressures. These pressures heat, melt and deform
the rocks. Such meteorites are said to be "shocked" (Wiki).
Carbonaceous chondrites (also known as C-type chondrites) are characterised by the presence of carbon
compounds.
CH (high metal) carbonaceous chondrites are rich in metallic Fe–Ni, and have a higher proportion of metal than all
other chondrite groups.
CM (Mighei type) chondrites are composed of about 70% fine-grained material (matrix), and most have experienced
extensive aqueous alteration.
CV (Vigarano type) chondrites are characterized by mm-sized chondrules and abundant refractory inclusions set in a
dark matrix that comprises about half the rock. CV chondrites are noted for spectacular refractory inclusions, some
of which reach centimetre sizes, and they are the only group to contain a distinctive type of large, once-molten
inclusions.
(Wiki)
Stony-iron meteorites consist of nearly equal parts of meteoric iron (kamacite,
taenite and tetrataenite) and silicates
(Wiki).
Mesosiderites are a class of stony–iron meteorites consisting of about equal parts of metallic
nickel-iron and silicate.
They are breccias with an irregular texture; silicates and metal occur often
in lumps or pebbles as well as in fine-grained intergrowths. The silicate part contains
olivine, pyroxenes and calcium-rich
feldspar
(Wiki)
Iron meteorites consist overwhelmingly of meteoric iron, an alloy usually of
kamacite and taenite
(Wiki).
Angrites are a rare group of achondrites consisting mostly of Al-Ti bearing
diopside, hedenbergite,
olivine, anorthite and
troilite with minor traces of phosphate and metals
(Wiki).
Ataxites are a class of iron meteorites with a high nickel content, usually over 18%, and that show no
Widmanstätten patterns upon etching
(Mindat).
Shergottite meteorites are Martian meteorites comprising basalt
and gabbro formed from subalkaline magmas
(Mindat).
Pallasite consists of centimetre-sized olivine crystals in an
iron-nickel matrix. Coarser metal areas
develop Widmanstätten patterns upon etching. Minor constituents are
schreibersite, troilite,
chromite, pyroxenes and the phosphates
whitlockite, stanfieldite,
farringtonite and merrillite
(Wiki).
Ureilites, named after the Novo-Urei, Russia, fall of 1886, are
ultramafic achondrites that contain interstitial carbon as
graphite or diamond. The majority
consist of olivine + uninverted
pigeonite. In a few, the
pyroxene is augite and/or
orthopyroxene instead. In addition, about 10% of ureilites are polymict
(containing multiple types of rock)
breccias, containing a few percent of
feldspathic material in addition to typical ureilitic components
(Mindat).
Tektite is a natural glass formed from a meteorite impact melting the local rock
(Mindat).
Maskelynite is a type of naturally occurring glass having the composition of a
plagioclase feldspar, created by the vitrification of plagioclase by
shock melting in meteorites and meteorite impacts
(Mindat).