Hyalopilitic
Volcanic groundmass fabric comprising abundant feldspar microlites with glassy interstitial material; IODP usage emphasizes aligned microlites.
Language and route: English/continental petrographic combination of Greek-derived hyalo- and pilitic. English/continental petrographic combination of Greek-derived hyalo- and pilitic
Literal gloss: glassy felt
The name and its history
Traditional petrographic descriptor; first inventor unverified · Traditional petrographic descriptor; first inventor unverified
- What does the word literally mean?
- Immediate route: English/continental petrographic combination of Greek-derived hyalo- and pilitic. Linguistic gloss: ‘glassy felt’. This gloss describes language, not a demonstrated early geological theory.
- What did the original author mean?
- Optical petrography extended felted-microlite terms to distinguish groundmass still rich in glass from its more thoroughly crystallised alternatives.
- Why was the name needed?
- An aligned or felted network of tiny crystals alone could not communicate whether the remaining lava matrix had crystallised.
- What evidence supported the original concept?
- Plagioclase microlites and identifiable glass in thin section; alignment is required in some protocols but not every older definition.
- How has geology changed the concept?
- Literature is not fully uniform about whether microlites must be subparallel or randomly felted; the site follows the stated IODP protocol and records the usage difference.
Further historical context
Optical petrography extended felted-microlite terms to distinguish groundmass still rich in glass from its more thoroughly crystallised alternatives.
An aligned or felted network of tiny crystals alone could not communicate whether the remaining lava matrix had crystallised.
Plagioclase microlites and identifiable glass in thin section; alignment is required in some protocols but not every older definition.
Literature is not fully uniform about whether microlites must be subparallel or randomly felted; the site follows the stated IODP protocol and records the usage difference.
Editorial qualification
IODP emphasis on alignment versus some older definitions allowing a random felted arrangement.
Related names
Pilotaxitic · Intersertal · Trachytic texture · Microlite (petrographic)
Sources
- International Ocean Discovery Program, Expedition 360 methods — Operational definitions for igneous groundmass, flow and inclusion textures
- Geological Survey of India, Rock Texture Atlas — Photomicrographs and modern texture definitions