Petrology

Euhedral

crystals have well-developed faces

Subhedral

Crystals have some well-developed faces

Anhedral

crystals have no well-developed faces. 

Porphyritic Texture

describes an igneous rock texture characterized by the presence of larger, distinct crystals (phenocrysts) embedded in a finer-grained matrix (groundmass).

Amygdaloidal

a texture in volcanic rocks where gas bubbles (vesicles) trapped during cooling are later filled with secondary minerals

Petrology

Branch of geology dealing with the origin, occurrence, structure and history of rocks

Color Index

gives us an insight on the composition of the igneous rocks

Leucocratic

Light-colored rock means Felsic

Mesocratic

Medium-colored means Intermediate

Melanocratic

Dark-colored means Mafic

Hypermelanic

Very dark-colored means Ultramafic

Aphanitic

crystals too fine-grained to be visible to the naked eye which implies fast cooling near the earths surface with many small crstals

Microcrystalline

materials have crystals that are small but visible under a microscope

Cryptocrystalline

materials have crystals so tiny they are not distinguishable even with a microscope.

Phaneritic

coarse grains are enough to be visible to the naked eye means slow cooling at depth

fine grained

average crystal diameter is 1mm

Medium-graned

average crystal diameter is 1 to 5 mm

Coarse-grained

average crystal diameter is more than 5 mm

Equigranular

crystals have approximately the same grain size due to uniform growth rates of grains

Inequigranular

crystal grains vary considerably; due to variable growth rates of grains

Glomeroporphyritic

phenocrysts of the same or different minerals occurring clusters

Phaneroporphyritic

the groundmass exhibits phaneritic texture

Aphanoporphyrytic

the groundmass exhibits aphanitic texture

Holocrystalline

degree of crystallinity of igneous rocks that has all crystal appearance

Hypocrystalline

degree of crystallinity of igneous rocks that has both crystals and glass, with crystals dominating over glass appearance

Hypohyaline

degree of crystallinity of igneous rocks that has containing both crystals and glass with glass dominating over crystals appearance

Holohyaline

degree of crystallinity of igneous rocks that has all glass appearance

Idiomorphic (panidiomorphic)

Most grains of the igneous rock are euhedral

Hypidiomorphic

Most grains of the igneous rocks are subhedral and some are irregular and well-formed

Allotriomorphic (xenomorphic)

Most grains of the igneous rock are anhedral

Glassy

Igneous rock texture that has no crystals

Microlites or Crystallites

refers to the very small crystals embedded in glass

Vesicular

igneous rock texture that contains vesicle as a result of escape of gas

Amygdaloidal

igneous rock texture that has vesicles that have been filled with material

Amygdule

it is a vesicle that has been refilled

Pumiceous

an igneous rock texture with abundant vesicles comprising of more than 50% of the rock and will float in water

Scoriaceous

an igneous rock texture with abundant vesicles that comprise more than 50% of the rock and will sink in the water

Spherulitic

an igneous rock texture that is radial intergrowths of fibrous minerals

Graphic

an igneous rock texture consisting of intergrowths of quartz and alkali feldspar wherein the orientation of the quartz grains resembles cuneiform writing

Trachytoid

an igneous rock texture that has elongated minerals are preferentially aligned along a single direction

Layering/lineation

an igneous rock texture that has crystal form bands with a dominant mineral in each band

Flow banding

an igneous rock texture that is alternating layers in a lava flow caused by magma mingling

Magma mingling

the physical mixing of two or more magmas without significant chemical exchange.

Miarolitic

an igneous rock texture consists of cavities into which euhedral crystals which occurs in plutonic rocks

Fiamme

an igneous rock texture which is flattening of welded materials in a pyroclastic rock

Pyroclastic or Fragmental

an igneous rock texture formed when volcanic materials are extruded violently due to eruption or collapse which is made of glass, crystals or rock fragments

Mineral Assemblage

Mineral components occurring together in the same rock

Percent abundance

it is based on visual estimate of the volume of the observed component against the volume of the whole rock

Total Alkalis Versus Silica (TAS)

If the mineral mode cannot be determined often the case for volcanic rocks, we use

Contact Metamorphism

this type of metamorphism, the magma invades the pre-existing rock creates a zone of alteration (aureole) around the intruding body. Affects upper crustal (<10km) country rock

Contact Metamorphism

this type of metamorphism has high temperature but low pressure which results in non-foliation of rocks

Contact Metamorphism

example of metamorphic rocks in this type of metamorphism is hornfels and granofels

Regional (Dynamothermal) Metamorphism

Majority of metamorphic rocks are formed during mountain building where large segments of crust are deformed

Regional Metamorphism

This type of metamorphism has high pressure and high temperature which results in foliated rocks and foliation at high angle bedding planes

Regional Metamorphism

What type of metamorphism is the setting of palawan-mindoro vs. philippine mobile belt?

Regional Metamorphism

The example of metamorphic rocks found in this type of metamorphism is slate, phyllite, schist, gneiss

Burial Metamorphism

This type of metamorphism is caused by massive amounts of materials accumulating in a subsiding basin, causing low-grade metamorphism at the deepest layers

Burial Metamorphism

The metamorphic rocks are non-foliated rocks due to relatively low temperature and the metamorphism transpires after diagenesis

Hydrothermal Metamorphism

Rocks are altered as result of high temperature and moderate pressures due to the the presence of hydrothermal fluids, typically high temperature with moderate pressure

Dynamic/ Fault Zone Metamorphism

Occurs primarily due to non-uniform (deviatoric) stress in fault zones and shear zones resulting to weakly foliated rock ex: mylonite

Impact Metamorphism

Occurs when high-speed projectiles called meteorites strike the Earth’s Surface; high temperature and high pressure over a short period of times

Impact Metamorphism

example of the rocks found in this metamorphism is impactites, suevite, tektite

Slaty Cleavage

a type of texture associated with low-grade metamorphism cleavage typical in fine-grained, low-grade metamorphic rocks where grains are too small

Grenulation

a type of texture associated with low-grade metamorphism Closely-spaced regular folds at a small scale

Schistosity

a type of foliation found in certain metamorphic rocks, characterized by the alignment of platy minerals, such as mica.

Gneissic Layering

This type of metamorphic texture has compositional layering showing alternating light and dark layers. Generally coarsed-grained

Lepidoblastic

Texture that is associated with foliation which platy minerals like mica and chlorite are aligned along a preferred orientation, example of which is slate, phyllite and schist

Nematoblastic

Texture that is associated with foliation which elongated minerals like sillimanite and amphibole are aligned along a preferred orientation example of which are mica-poor amphibolites

Metamorphic Grade

Convenient term that is commonly used to express the general increase in degree of metamorphism without specifying the exact relationship between temperature and pressure

Prograde Metamorphism

Changes to rocks due to increasing metamorphic grade

Retrograde Metamorphism

the process where rocks formed under high-temperature and pressure conditions are transformed into rocks more stable at lower temperatures and pressures.

Porphyroblastic

texture related to grain size of metamorphic rock where larger minerals occuring in a groundmass of small crystals

Relict Texture

texture related to grain size of metamorphic rock where clast/fragment from the original rock was not completely deformed/replaced after metamorphism

Granoblastic

texture related to similar grains of metamorphic rocks that has no schistosity and crystals are of equal sizes

Granofelsic

Texture related to similar grains of metamorphic rocks that is coarse-grained texture where grains are interlocking

Hornfelsic

a type of texture found in metamorphic rocks, specifically those formed through contact metamorphism. It's characterized by a very fine-grained, dense, and non-foliated (lacking layers) appearance

Mesh

Texture related to similar grains of metamorphic rocks that has network of interwoven serpentine minerals

Cataclastic

Texture related to similar grains of metamorphic rocks that is characterized by angular porphyroclastic and lithic fragments in a matrix of similar composition

Mylonitic

Texture related to similar grains of metamorphic rocks that has very fine crystal and layering, resulting to usually very smooth surface

Biotite-kyanite schist

Metamorphic rock with schistosity and has less biotite than kyanite

Calcite Granofels (Marble or Skarn)

Metamorphic rock with granofelsic texture and is composed of calcite

Metabasalt

What is the name for low-grade metamorphic rock mostly basalt in composition?

Barrovian Zones of Metamorphism

A series of metamorphic zones characterized by the progressive appearance of index minerals in pelitic rocks (those derived from clay-rich sediments) as metamorphic grade (temperature and pressure) increases

Clasts, matrix, cement

What are the main components of sedimentary rocks?

Boulder

Based on udden-wentworth scale, what is the size class of clast with 4096 mm?

Cobble

Based on udden-wentworth scale, what is the size class of clast with 256mm?

Pebble

Based on udden-wentworth scale, what is the size class of clast with 64 mm?

Granule

Based on udden-wentworth scale, what is the size class of clast with 4mm?

Very coarse sand

Based on udden-wentworth scale, what is the size class of clast with 1 mm?

Coarse sand

Based on udden-wentworth scale, what is the size class of clast with 0.50mm?

Medium Sand

Based on udden-wentworth scale, what is the size class of clast with 0.25mm?

Fine sand

Based on udden-wentworth scale, what is the size class of clast with 0.125 mm?

Very fine sand

Based on udden-wentworth scale, what is the size class of clast with 0.0625mm?

Coarse Silt

Based on udden-wentworth scale, what is the size class of clast with 0.031mm?

Medium Silt

Based on udden-wentworth scale, what is the size class of clast with 0.0156 mm?

Fine Silt

Based on udden-wentworth scale, what is the size class of clast with 0.0078 mm?

Clay (Mud)

Based on udden-wentworth scale, what is the size class of clast with 0.000006 mm?

Rudites

sedimentary rocks that are gravel-dominated (>2mm clasts)

Monomictic orthoconglomerate

a type of sedimentary rock characterized by rounded, gravel-sized clasts (fragments) of a single rock type where the clasts are in contact with each other and supported by a matrix that fills the spaces between them

Polymictic orthoconglomerate

a type of sedimentary rock composed of rounded rock fragments (clasts) of various rock types where the clasts are in contact with each other and surrounded by a finer-grained matrix