Igneous Textural Term

Holocrystalline

Consisting entirely of crystals.

Hypocrystalline

Containing both crystals and glass.

Holohyaline

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.

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