Igneous Textural Term

Holocrystalline Consisting entirely of crystals (default term, not commonly used).

Hypocrystalline Containing both crystals and glass.

Holohyaline vitric Consisting entirely of glass.

Aphanitic Having minerals too fine grained to see with the naked eye.

Phaneritic Having minerals coarse enough to see with the naked eye.

Cryptocrystalline Having minerals too fine grained to distinguish microscopically.

Fine grained Having an average crystal diameter less than 1 mm.

Medium grained Having an average crystal diameter 1–5 mm.

Coarse grained Having an average crystal diameter greater than 5 mm.

Very Coarse Grained Having an average crystal diameter greater than 50 mm.

Pegmatitic Being very coarse grained (historically associated with very coarse granitoid rocks: pegmatites).

Saccharoidal Being fine- to medium-grained xenomorphic and equigranular (looking like sugar).

Aplitic A synonym for saccharoidal, but typically restricted to leucocratic granitoid rocks.

Equigranular Having grains that are all approximately the same size.

Inequigranular Having grains that vary considerably in size.

Porphyritic Having approximately bimodal size distribution (usually requires a great difference).

Megaporphyritic Having a porphyritic texture that can be seen in hand specimen (rarely used).

Microporphyritic Having a porphyritic texture that is visible only under the microscope.

Phyric (-phyric) An adjective (or suffix) referring to porphyritic texture.

Phenocryst A large crystal set in a fine matrix.

Microphenocryst A microscopic crystal that is larger than the remainder of the groundmass.

Megacryst An unusually large crystal, either a phenocryst or a xenocryst.

Poikilitic The state of a host phenocryst (oikocryst) containing many inclusions of other minerals.

Oikocryst A host phenocryst in poikilitic texture.

Groundmass (matrix, mesostasis) The glassy or finer-grained element in the porphyritic texture.

Cumulophyric Having phenocrysts of the same or different minerals occurring in clusters.

Glomeroporphyritic Synonymous with cumulophyric (used by some to specify that only one mineral is involved).

Hiatial porphyritic Having a pronounced difference in size between the phyric and groundmass phases (the default term: rarely used).

Seriate Having a continuous gradation in size.

Aphyric Not porphyritic (having no phenocrysts)

Euhedral (idiomorphic) Completely bounded by crystal faces.

Subhedral (subidiomorphic) Having crystal faces that are only partially developed.

Anhedral (allotriomorphic) Having crystal faces that are entirely absent.

Crystal habits: equaint, prismatic, columnar, accicular, fibrous, tabular, platy, micaceous, lath-shaped, etc.

Corroded (embayed) Subhedral or anhedral and produced by partial melting (resorption) of phenocrysts by the melt

Panidiomorphic Having a majority of euhedral grains. Rare.

Hypidiomorphic Consisting predominantly of subhedral grains. Common in many granitic rocks.

Allotriomorphic Having a majority of anhedral grains (common).

Sutured Characterized by articulation along highly irregular interpenetrating boundaries. Common in recrystallized deformed rocks.

Mosaic A texture of polygonal equigranular crystals.

Host (Oikocryst) A large mineral that includes others in poikilitic texture.

Guest The included mineral in poikilitic texture.

Poikilitic Containing several small discrete crystals of another mineral. Refers to growth phenomena, not exsolution or replacement.

Graphic Having an intergrowth in which the guest shows angular wedge-like forms. Usually occurs with quartz in microcline.

Micrographic Having graphic texture that is visible only under the microscope.

Granophyric Having a texture in which the quartz and feldspars penetrate each other as feathery irregular intergrowths. Resembles micrographic texture but is more irregular.

Exsolution lamellae Lamellar bands of a phase exsolved from a host phase.

Perthitic Having irregular veins, patches, lenses, etc., of sodic plagioclase in an alkali feldspar host. Usually results from exsolution.

Antiperthitic Having exsolution lamellae of alkali feldspar in a plagioclase host. Usually much thinner than perthite.

Symplectite A replacement texture in which a mineral is replaced by an intergrowth of one or more minerals.

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

Spherulitic Having a radial intergrowth of fibrous minerals. Commonly alkali feldspar and quartz in devitrified silicic volcanics.

Axiolitic Similar to spherulitic, but with fibers occurring in a layer and oriented normal to its walls.

Variolitic Spherulitic and consisting of divergent plagioclase fibers. Applies to certain basalts.

Coalescent Having anhedral texture developed by simultaneous growth of two mineral grains in contact.

Ophitic Having large pyroxene grains enclosing small, random plagioclase laths (Figure 8).

Subophitic Having plagioclase laths that are larger and only partially enclosed by the pyroxene.

Nesophitic Having a plagioclase that is larger, with interstitial pyroxenes.

Intergranular Having small, discrete grains of pyroxene, olivine, etc., filling the interstices in a random network of larger plagioclase laths.

Intersertal Having glass, cryptocrystalline material, or alteration products occupying the spaces between plagioclase laths.

Hyalo-ophitic Having an intersertal texture in which a larger amount of glass is present than pyroxene.

Hyalopilitic Having a large amount of glass, with plagioclase occurring only as tiny, random microlites.

Diktytaxitic The texture of certain volcanics in which bounding crystals protrude into abundant angular interstitial gas cavities.

Cumulate Displaying interstitial growth of a mineral between earlier ones that are all in contact and give the distinct impression that they accumulated at the bottom of a magma chamber.

Orthocumulate Having cumulate texture, with other minerals occupying the interstitial areas.

Adcumulate Having cumulate texture in which the early cumulate minerals grow to fill the pore space

Mesocumulate Having a texture that is intermediate between ortho- and adcumulate.

Pseudomorph A replacement texture in which one or more minerals replace another, retaining the form of the original mineral.

Symplectite A replacement texture in which a mineral is replaced by an intergrowth of one or more minerals.

Uralitization Replacement of pyroxene by amphibole.

Saussuritization Replacement of plagioclase by epidote.

Biotitization Replacement of pyroxene or amphibole by biotite.

Chloritization Replacement of any mafic mineral by chlorite.

Seritization Replacement of feldspar or feldspathoids by fine white micas.

Interstitial Having one mineral filling the interstices between earlier crystallized grains (Figure 7).

Crystallites Minute, inchoate crystals in the 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 determinable.

Felty Consisting of random microlites (Figure 13b).

Pilotaxitic A synonym for felty.

Trachytic Consisting of (feldspar) microlites aligned due to flow.

Embayed Having embayments due to reaction with the melt (resorption).

Skeletal Having crystals that grew as, or have been corroded to, a skeletal framework with a high proportion of internal voids.

Sieve Crystals 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 Containing gas bubbles.

Scoriaceous Highly vesicular.

Pumiceous Having a frothy vesicular structure characteristic of pumice.

Miarolitic Having gas cavities into which euhedral minerals protrude. Applies to certain plutonic rocks.

Pipe vesicles Tubelike elongate vesicles that result from rising gases.

Vesicular pipes Cylindrical bodies that are highly charged with vesicles.

Amygdaloidal Having vesicles that are completely or partially filled with secondary minerals.

Lithophysae Large ovoid structures representing gas bubbles in devitrified rhyolitic glass.

Foliation Planar parallelism.

Banding Alternating planar layers.

Lineation Linear parallelism.

Xenolith An inclusion of country rock.

Xenocryst A single-crystal foreign inclusion.

Perlitic Having a concentric fracture pattern resulting from contraction of some volcanic glasses upon cooling.

Pyroclastic Composed of fragments.

Ocelli Ovoid blobs created by liquid immiscibility, mingled magmas, or filled vesicles.

Orbicules Ovoid masses of radiating crystals, commonly concentrically banded, found in some granites.

Spinifex A centimeter-scale texture subparallel to dendritic growth of olivine crystals in some quenched ultramafics.

Pele’s tears Glassy lapilli.

Pele’s hair Hair-like strands of glass.

Fiamme Compressed pumice fragments in a tuff.