spotted slate

spotted slate

[′späd·əd ′slāt]
(petrology)
A type of slate containing dark spots that represent the beginning of porphyroblast development.
References in periodicals archive ?
This group matches the grey bracers (spotted slates) minus Aldbourne (9) but plus the two 'probable' spotted slate pieces.
This group precisely matches the set of grey bracers including the possible spotted slates.
Firstly, most of the arched types (C1) and the most elaborate of the flat types (B3) were made from the green Langdale rock, whilst the bracers made from the spotted slates were all flat items belonging to Type B.