Stone in Archaeology Database


Portland Roach

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Local Name(s): Portland Roche,
Portland Roach.
Example of Portland Roach
Stone Group: Sedimentary
Stone Type: Limestone
Geology:
Era:   Mesozoic
Period:   Jurassic
Epoch:   Upper
Geological Sub-Divisons:

Portland Formation, Portland Stone Member (Portland Stone). Three main beds are important:- Roach (normally top of the series), Whit Bed (middle) and Base Bed (lower).

General Colour Description:

Portland Roach is buff, cream or grey/cream in colour when fresh, but has a tendency to become white on exposure.

Hand Specimen Description:

A coarse textured, shelly, oolitic limestone honeycombed by empty moulds and casts of aragonitic fossil shells such as the cerithid gastropod aptyxiella portlandica ('portland screws') and the bivalve trigonia gibbosa ('orses 'eds'). These shells are elongated to rounded and can extend up to 6mm across. The finer grained portion of this stone is very similar to Whit Bed formed from micrite ooids with a small quantity of micrite occurring as matrix.

Stone Identifiers: Fossiliferous,  Oolitic.
Reacts dilute to HCl? Yes