Amygdaloidal
A volcanic-rock texture characterised by former gas vesicles that have been partly or wholly filled by secondary minerals.
Language and route: English adjective associated with amygdaloid/amygdule, ultimately from Greek via Latin and French in some lexical routes. English adjective associated with amygdaloid/amygdule, ultimately from Greek via Latin and French in some lexical routes
Literal gloss: almond-shaped infilled cavities
The name and its history
Historic common geological adjective; first use unverified · Historic common geological adjective; first use unverified
- What does the word literally mean?
- Immediate route: English adjective associated with amygdaloid/amygdule, ultimately from Greek via Latin and French in some lexical routes. Linguistic gloss: ‘almond-shaped infilled cavities’. This gloss describes language, not a demonstrated early geological theory.
- What did the original author mean?
- The historic noun amygdaloid labelled spotted volcanic rocks with almond-like mineral-filled voids before rock-composition classifications were standardised.
- Why was the name needed?
- A need to distinguish secondary mineral-filled cavities from unfilled vesicles and from primary igneous crystals.
- What evidence supported the original concept?
- Almond-like calcite, quartz, chalcedony or zeolite fillings in cavities of basalt and related lavas; historical meaning often applied to a rock variety.
- How has geology changed the concept?
- The adjective describes a fabric regardless of modern rock name; many amygdules are rounded rather than strictly almond-shaped.
Further historical context
The historic noun amygdaloid labelled spotted volcanic rocks with almond-like mineral-filled voids before rock-composition classifications were standardised.
A need to distinguish secondary mineral-filled cavities from unfilled vesicles and from primary igneous crystals.
Almond-like calcite, quartz, chalcedony or zeolite fillings in cavities of basalt and related lavas; historical meaning often applied to a rock variety.
The adjective describes a fabric regardless of modern rock name; many amygdules are rounded rather than strictly almond-shaped.
Editorial qualification
Do not conflate an original vesicle and its later secondary mineral filling.
Related names
Sources
- Geological Survey of India, Rock Texture Atlas — Photomicrographs and modern texture definitions
- British Geological Survey, Ballantrae memoir glossary — Historic descriptions of porphyritic rock and textural terminology