Terminology
|
Abbreviation
|
Definition
|
|---|---|---|
| Contact: | ||
| Distinct | cg | Contact featuring clearly separated glassy pahoehoe surfaces |
| Annealed, fused | ca | Contact between lobes is marked by a centimeter-thick glassy band formed by fusion of the original lobe surfaces |
| Discontinuous | cd | Contact between lobes dissipates or disappears when followed in outcrop |
| Vesiculation structure: | ||
| Vesicles | ve | Molds of gas-filled voids frozen in the lava and are referred to as microscopic (<2 mm diameter) or macroscopic (>2 mm diameter) |
| Diktytaxitic texture | vd | Microscopic (<2.0 mm), irregular intercrystalline voids and outlined by crystal faces of adjacent groundmass minerals (Fuller, 1931) |
| Segregation vesicle | sv | Vesicles lined by segregated material |
| Pipe vesicles andvesicle cylinders | pvvc | Roughly cylindrical pipes of near-vertical orientation that are hollow (pv) or filled with vesicular segregated material (vc) |
| Horizontal vesicle sheets | hvs | Sheets of vesicular segregated material, centimeters to tens of centimeters thick, that are continuous (>50 m long) and discontinuous (1-10 m long) on an outcrop scale; these sheets were previously identified as segregation veins or vesicle sheets (e.g. Goff, 1996) |
| Megavesicles | mv | Dome-shaped voids with flat floors and arched to dome-shaped roofs; their dimensions range from several to tens of centimeters; they are floored by moderately vesicular to nonvesicular segregated material and occur in close association with horizontal vesicle sheets |
| Vesicular zone | hvz | Decimeter- to meters-thick horizons with high concentrations (>10 vol%) of macroscopic vesicles |
| Petrographic texture: | ||
| Crystallinity | c, hc, hyh, G | Relative abundance of crystals vs. glassy mesostasis is indicated by holocrystalline (c [crystallinity = 90%-100%]), hypocrystalline (hc [50%-90%]), hypohyaline (hyh [10%-50%]), or holohyaline (G [0%-10%]) |
| Granularity | Crystal size of the lava groundmass (See Table T5) | |