Stone in Archaeology Database

Harnage Slate

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Local Name(s): Harnage Slate,
Hoar Edge Grit.
Example of Harnage Slate
Stone Group: Sedimentary
Stone Type: Sandstone
Era:   Palaeozoic
Period:   Ordovician
Epoch:   Lower
Geological Sub-Divisons:

Hoar Edge Grit. Basement Beds of the Caradoc Series.

General Colour Description:

A yellow/brown colour with moderate flecks of cream/yellow.

Hand Specimen Description:

There are two beds, firstly a medium grained, hard, granular sandstone which is well sorted with a rough feel (sample in our collection) the second, a shelly, coarse textured stone which splits along the fossil shells of a brachiopod called Heterorthis subquadrata (Stone Roofing Association: n.d.[a]). Harnage slate is hard and compact at depth, but where it is close to the surface post-glacial weathering has weakened it along the bedding planes inducing a plane of parting. It is this natural parting which renders the rock suitable for roofing. The depth of weathering is no more than about 2 metres in any of the exposures (Lawson 1985: 116-118).

Stone Identifiers: Granular.
Reacts dilute to HCl? No