Common Igneous Textural Terms and photomicrographs


Terminalogy Definiton Thin-section #



Consisting entirely of crystals.



Containing both crystals and glass

BH250-19, BH250-89

Holohyaline, Vitric

Consisting entirely of glass  

Grain Size



Most minerals are too fine-grained to see with the naked eye BH250-60, -74, -89


Minerals are coarse enough to see with the naked eye BH250-11


Too fine-grained to distinguish the minerals microscopically  

Fine grained

Average crystal diameter is less than 1 mm BH250-49

Medium grained

Average crystal diameter is 1-5 mm BH250-11, -46

Coarse grained

Average crystal diameter is greater than 5 mm BH250-50


Very coarse grained PegmatiticBlackHills1, 2


Fine- to medium-grained xenomorphic and equigranular.



Grains are all approximately the same size BH250-41
Inequigranula Grains vary considerably in size BH250-50

Porphyritic Textures


Approximately bimodal size distribution.



Porphyritic texture that can be seen in hand specimen.

BH250-11, -50


Porphyritic texture that is visible only under the microscope  
Phyric An adjective (or suffix) referring to porphyritic texture  


Large crystal set in a fine matrix BH250-8, -60, -72, -82, -83, -86


Microscopic crystals that are still larger than the remainder of the groundmass BH250-60


An unusually large crystal, either a phenocryst or a xenocryst BH250-8


The host phenocryst (oikocryst) contains many inclusions of other minerals BH250-11, -50, 83


The host phenocryst in poikilitic texture BH250-11


The glassy or finer grained element in the porphyritic texture (matrix)

BH250-15, -60, -80, -82, -83, -85, -88


Phenocrysts of the same or different minerals occur in clusters BH250-85


Synonymous with cumulophyric.


Hiatial porphyritic

There is a pronounced difference in size between the phyric and groundmass phases.

Seriate There is a continuous gradation in size  
Aphyric Non-porphyritic (phenocrysts absent)  

Form of Indvidual Grains

Euhedral (idiomorphic)   Completely bounded by crystal faces BH250-41
Subhedral (subidiomorphic) Crystal faces only partially developed BH250-11
Anhedral (allotriomorphic) Crystal faces are entirely absent  
Corroded (embayed)      Subhedral or anhedral forms produced by partial melting (resorption) of phenocrysts by the melt  
Crystal habits equaint, prismatic, columnar, accicular, fibrous, tabular, platy, micaceous, lath-shaped, etc.  

Forms of Grains in the Rock

Panidiomorphic  Most of the grains are euhedral. BH250-41
Hypidiomorphic Consisting predominantly of subhedral grains BH250-11
Allotriomorphic Most of the grains are anhedral  

Characterized by articulation along highly irregular inter-penetrating boundaries. Common in recrystallized de-formed rocks

BH250-27, BH250-13, BH250-21

A texture of polygonal equigranular crystals



Host (Oikocryst) The large mineral that includes others in poikilitic texture BH250-11,-50, -86
Guest The included mineral in poikilitic texture BH250-86

One large crystal contains several small discrete crystals of another mineral. Refers to growth phenomena, not exsolution or replacement.

BH250-11, -50
Graphic An intergrowth in which the rock shows angular wedge-like forms. Usually occurs with quartz in microcline BH250-92
Micrographic Graphic texture visible only under the microscope  

A texture of certain porphyritic rocks in which the groundmass minerals (usually quartz and alkali feldspar) penetrate each other as feathery irregular intergrowths. Resembles micrographic texture, but is more irregula

Exsoiution lamellae       Lamellar bands of a phase exsolved from a host phase BH250-9 BH250-92, BH250-81
Perthitic Irregular veins, patches, lenses, etc., of sodic plagioclase in an alkali feldspar host. Usually results from exsolution BH250-81 BH250-92
Antiperthitic Exsolution lamellae of alkali feldspar in a plagioclase host. Usually much thinner than perthite BH250-81
Symplectite A replacement texture in which a mineral is replaced by an intergrowth of one or more minerals.  

A secondary texture consisting of irregular "wormy" blebs or rods of quartz in a plagioclase host adjacent to alkali feldspar grains

BH250-13 BH250-49
Spherulitic A radial intergrowth of fibrous minerals. Commonly alkali feldspar and quartz in devitrified silicic volcanics BH250-85
Axiolitic Similar to spherulitic, but the fibers occur in a layer and are oriented normal to its walls BH250-85


Spherulitic structures consisting of divergent plagioclase fibers in certain basalts.



Anhedral textures developed by simultaneous growth of two mineral grains in contact  

Textures of Mafic Igneous Rocks



Large pyroxene grains enclose small random plagioclase laths BH250-11, -50


The plagioclase laths are larger and only partially enclosed by the pyroxene BH250-11, -50


Plagioclase is larger yet and the pyroxenes are interstitial BH250-11, -50


Small discrete grains of pyroxene, olivine, etc., fill the interstices in a random network of larger plagioclase laths



Glass, cryptocrysialline material, or alteration products occupy the spaces between plagioclase laths BH250-11


An intersertal texture in which a larger amount of glass is present and less pyroxene  


Still more glass is present and plagioclase occurs only as tiny random microlites.



Texture of certain basalts containing abundant angular interstitial gas cavities between the plagioclase laths  


Interstitial growth of a mineral between earlier ones which are all in contact and give the distinct impression that they accumulated at the bottom of a magma chamber

Orthocumulat Cumulate texture with other minerals occupying the interstitial areas  
Adcumulate Cumulate texture in which the early cumulate minerals grow to fill the pore space  


Intermediate between ortho- and adcumulate  

Replacement Textures

Pseudomorph One or more minerals replace another, retaining the form of the original mineral BH250-50, -60
Symplectite A replacement texture in which a mineral is replaced by an intergrowth of one or more minerais BH250-48
Uralitization Replacement of pyroxene by amphibole  
Saussuritization Replacement of plagioclase by epidote  
Biotitization Replacement of pyroxene, amphibole or granet by biotite  
Chloritization Replacement of any mafic mineral or garnets by chlorite BH250-49

Replacement of feldspar or feldspathoids by fine white micas. Miscellaneous Terms


Miscellaneous Terms

Interstitial One mineral fills the interstices between earlier crystallized grains BH250-11

Minute, inchoate crystals in earliest stages of formation. They are isotropic and cannot be identified under the microscope

Microlites Tiny needle- or lath-like crystals of which at least some properties are microscopically detenninable  
Felty Consisting of random microlites  
Pilotaxitic Like felty  
Trachytic Consisting of (feldspar) microlites aligned due to flow  
Embayed Having embayments due to reaction with the melt (resorption)  
Skeletal Crystals which grew as, or have been corroded to, a skeletal framework with a high proportion of internal voids  
Sieve Crystals are filled with channelways (appearing as holes) due to resorption  
Epitactic Oriented nucleation of one mineral on another of a different kind  
Rapakivi Overgrowths of plagioclase on alkali feldspar  
Vesicular Contains gas bubbles BH250-60, -82, -84
Scoriaceous Highly vesicular  

Frothy vesicular structure characteristic of pumice

Diktytaxitic Containing vesicles into which microphenocrysts protrude  
Miarolitic Gas cavities present in certain plutonic rocks into which euhedral minerals protrude  
Pipe vesicles             

Tube-like elongate vesicles that result from rising gases

See photo
Vesicular pipes Cylindrical bodies highly charged with vesicles  
Amygdaloida Vesicles completely or partially filled with secondary minerals BH250-85
Lithophysae Large ovoid structures representing gas bubbles in devitrified rhyolitic glass  
Flow A parallel structure developed as the result of flow  
Foliation Planar parallelism BH250-26, BH250-52, BH250-66, BH250-20, BH250-21, BH250-22, BH250-26 BH250-66, BH250-67
Banding Alternating planar layers  
Lineation Linear parallelism  
Xenolith An inclusion of country rock BH250-112
Xenocryst A single-crystal foreign inclusion BH250-112
Perlitic Concentric fracture pattern resulting from contraction of some volcanic glasses upon cooling BH250-92, BH250-81
Pyroclastic Comprised of fragments BH250-19
Ocelli  Ovoid blobs created by liquid immiscibility, mingled magmas, or filled vesicles  
Orbieules Ovoid masses of radiating crystals, commonly concentrically banded, found in some granites  
Spinifex Centimeter-scale sub-parallel to dendritic growth of olivine crystals in some quenched ultramafics BH250-87

Pyroclastic Terms

Pele's tears                 Glassy lapilli  
Fiamme Compressed pumice fragments in a tuff