Petrographic Texture

Question 1

Phenocrysts lie in a matrix of glass

Answer 1

Vitrophyric

Question 2

Groundmass is a dense overgrowth of quartz and feldspar

Answer 2

Felsophyric

Question 3

Groundmass is made up of rectangular formed feldspar instead of lath slender lath crystals

Answer 3

Orthophyric

Question 4

Phenocrysts in a porphyritic texture are clustered into aggregates called glomerocrysts or crystal clots which indicates crystal fractionation by crystal settling

Answer 4

Glomeroporphyritic

Question 5

Phenocrysts contain small grains of other minerals, enclosing them, indicating that the smaller grains may have crystallized first.

Answer 5

Poikilitic

Question 6

Variety of poikilitic texture where plagioclase laths are enclosed by pyroxenes or olivine.

Answer 6

Ophitic

Question 7

Variety of Ophitic wherein plagioclases enclose ferromagnesian minerals, indicating slower cooling in basaltic rocks

Answer 7

Subophitic

Question 8

Angular interstices between feldspars filled with glass Instead of pyroxene

Answer 8

Hyalophitic

Question 9

Also called corona, reaction rim and Rapakivi, displays a secondary mineral formed around another mineral, indicating a post-magmatic reaction

Answer 9

Opacitic

Question 10

Variety of opacitic where there is a secondary rim or corona

Answer 10

Kelyphitic

Question 11

Occurs where crystal occupies occupy spaces between at least two larger crystals, indicating a later formation

Answer 11

Intergranular

Question 12

Denotes that angular spaces between crystals are filled with glass, that may be devitrified or altered, and small crystals

Answer 12

Intersertal

Question 13

Holocrystalline groundmass with lath-shaped microlites, typically plagioclase, are generally oriented irregularly

Answer 13

Pilotaxitic

Question 14

Extrusive igneous rock texture wherein the groundmass flow in the direction of lava flow and around inclusions, and occurs in alkali-rich rocks

Answer 14

Trachytic

Question 15

Macroscopic variety of Trachytic that is visible to the naked eye

Answer 15

Trachytoid

Question 16

Or Symplectic, is an intergrowth of branching rods of quartz set in a single crystal of plagioclase

Answer 16

Myrmekitic

Question 17

Observed where a solid solution phase unmixes into two separate phases in the solid state, often occurring between two or more endmember compositions

Answer 17

Exsolution

Question 18

Intergrowth of plagioclase feldspar in alkali feldspar host

Answer 18

Perthitic

Question 19

Intergrowth of alkali feldspar in plagioclase feldspar host

Answer 19

Holocrystalline

Question 20

Contains 100% crystals

Answer 20

Hypocrystalline

Question 21

A mix of glass and crystals, but contains more crystals than glass

Answer 21

Hypohyaline

Question 22

contains 100% glass

Answer 22

Holohyaline / Vitric

Question 23

Contains very coarse grains having >30mm in diameter

Answer 23

Pegmatitic

Question 24

contains coarse-grained minerals

Answer 24

Phaneritic / Dyscrystalline

Question 25

contains fine-grained minerals

Answer 25

Aphanitic / Eucrystalline

Question 26

Too fined-grained to be distinguish minerals microscopically

Answer 26

Cryptocrystalline

Question 27

Displays grains that are generally equant

Answer 27

Granular

Question 28

Medium- to coarse-grained minerals, most of which are devoid of crystal faces

Answer 28

Granitic

Question 29

Contains equidimensional cryptocrystalline groundmass

Answer 29

Felsitic

Question 30

Variety of Poikilitic where in inclusions have a complete series of crystal sizes

Answer 30

Seriate