Allochem
A carbonate grain or component differentiated from the surrounding matrix/cement, such as an ooid, skeletal fragment, intraclast or pellet.
Language and route: English scientific shortening of allochemical constituent; allo- from Greek ἄλλος, ‘other’. English scientific shortening of allochemical constituent; allo- from Greek ἄλλος, ‘other’
Literal gloss: distinguished/other carbonate constituent
The name and its history
Robert L. Folk (1959 original scheme) · 1959 abstract and source record checked
- What does the word literally mean?
- Immediate source or formation: English scientific shortening of allochemical constituent; allo- from Greek ἄλλος, ‘other’. Literal gloss ‘distinguished/other carbonate constituent’. This linguistic evidence is distinct from claims about the namer’s intentions.
- What did the original author mean?
- The term identified carbonate particles that could be counted separately in thin sections to make descriptions reproducible and link textures to transport.
- Why was the name needed?
- It addressed the difficulty of describing limestones composed of mixtures of skeletons, ooids, intraclasts and pellets without reducing them to one genetic origin.
- What evidence supported the original concept?
- Folk’s original abstract enumerates four prominent types: intraclasts, oolites, fossils and pellets.
- How has geology changed the concept?
- The grouping is a petrographic convenience, not one depositional process; allochems can differ greatly in biology, environment and post-depositional change.
Further historical context
The term identified carbonate particles that could be counted separately in thin sections to make descriptions reproducible and link textures to transport.
It addressed the difficulty of describing limestones composed of mixtures of skeletons, ooids, intraclasts and pellets without reducing them to one genetic origin.
Folk’s original abstract enumerates four prominent types: intraclasts, oolites, fossils and pellets.
The grouping is a petrographic convenience, not one depositional process; allochems can differ greatly in biology, environment and post-depositional change.
Editorial qualification
Priority and exact original naming language not independently authenticated; distinguish documented later use from first coinage.
Related names
Ooid · Micrite · Sparite · Grainstone (carbonate) · Coquina
Sources
- Folk 1959, Practical Petrographic Classification of Limestones, AAPG Bulletin 43:1–38 — identified original publication; abstract directly inspected, not every page
- Dunham 1962, Classification of Carbonate Rocks According to Depositional Texture, AAPG Memoir 1:108–121 — identified original; author abstract directly inspected
- SEPM Strata, carbonate classification comparing Folk, Dunham and extensions — professional retrospective of distinct schemes and Embry–Klovan 1971 extension