Table T1. Groundmass textural terms, Leg 187.
| Textural term | Textural definition |
|---|---|
| Quench textures | |
| Glassy | Matrix is amorphous basaltic glass with no visible incipient crystallization. |
| Spherulitic | Texture is characterized by the presence of spherulites, which are spherical bodies that usually consist of radiating plagioclase and/or clinopyroxene microlites or crystals; individual crystals are indistinguishable with the microscope. These range from discrete spherulites (i.e., individual spherulites separated by glass) to coalesced spherulites (i.e., where spherulites are so abundant they are in contact with one another and the amount of glass is small). |
| Sheaf | A bundled arrangement of small crystals assuming sheaflike appearance; a central axis of growth often occurs. Sheaf texture ranges from immature (crystals cannot be individually distinguished with the microscope) to mature (discrete skeletal crystals can be distinguished with the microscope). Mineralogically, sheaf textures tend to be dominated by plagioclase. |
| Plumose | Plume or featherlike arrangement of microlites or crystals; may grade from immature to mature (as in sheaf texture) according to crystal size. Mineralogically, plumose textures tend to be dominated by clinopyroxene. |
| Groundmass textures | |
| Intersertal | A term applied to volcanic rocks wherein a base (mesostasis or glass and small crystals) fills the interstices between unoriented feldspar laths, the base forming a relatively small proportion of the rock. |
| Intergranular | A term applied to volcanic rocks in which there is an aggregation of grains of clinopyroxene, not in parallel optical continuity between a network of feldspar laths, that may be divergent, subradial, or subparallel. Distinguished from an intersertal texture by the absence of interstitial glass or other quenched phases filling the interstices between the feldspar laths. |
| Subophitic | Said of the ophitic texture of an igneous rock in which the feldspar crystals are approximately the same as the size of the pyroxene and are only partially included by them. |
| Ophitic | A term applied to textural characteristics in which euhedral or subhedral crystals of plagioclase appear to be entirely enclosed in anhedral to subhedral augite. |
Note: This table is also available in ASCII format.