| Reference | N7 |
| NAME | Portmadoc (riven) |
| TYPE | Slate |
| GEOLOGY | Ordovician. Llandeilo Series |
| COUNTY | Gwynedd |
| COLOUR | Blue/grey. Occasional pyrite flecks |
| TEXTURE | Extremely fine grained. Finely cleaved |
| BLOCK SIZE LXBXH (mm) | |
| SUITABILITY | Roofing, cladding, flooring and architectural |
| USES (1) | |
| USES (2) | |
| USES (3) | |
| USES (4) | |
| Stone Names |
| Intro: Portmadoc Welsh Slate (N6) – Stone Library (shu.ac.uk) |
| Intro: Portmadoc Welsh Slate (N7) – Stone Library (shu.ac.uk) |