Scottish Geology Website

The Rhynie Chert is a unique fossiliferous deposit, known to palaeontologists throughout the world. Discovered in the early 1900's, the deposit has yielded completely preserved early land plants and arthropods. Hot spring activity during the Devonian led to the formation of a siliceous sinter and it was this sinter that ensured the unique preservation of the flora and fauna. In addition, the hot spring activity was responsible for chemically altering the sinter and nearby lavas to result in small, but measurable quantities of gold enrichment.

The Rhynie Chert Member is found within the Dryden Flags Formation of a Lower Old Red Sandstone outlier in the Grampian Highlands (Dalradian). The chert is generally blue-black in appearance and exhibits textures common to siliceous sinters (e.g. laminated, brecciated, vuggy and geopetal). Plant species found, often in growth position, include some of the earliest known vascular plants (including Rhynia, Horneophyton and Asteroxylon). Blue-green algae have also been identified, as well as the World's earliest lichen. The arthropods found to date include a crustacean (Lepidocaris), the euthycarcinoid Heterocrania, together with mites (including Protocarus), an arachnid (Palaeocharinus), the oldest-known harbestman spider, the earliest known insect remains (springtail), centipedes and a eurypterid (Heterocrania).

A block of the Rhynie Chert

A block of the Rhynie Chert. © Nigel Trewin.

A block of the Rhynie Chertshown in close up

Rhynie Chert in close up - this view illustrates the stems of plants perfectly preserved in the chert. © Nigel Trewin.

The Rhynie Chert Locality

The Rhynie Chert Locality Site of Special Scientific Interest. © Scottish Natural Heritage.

Mineralisation resulting from the epithermal hot spring activity has led to the alteration of andesitic lavas and the sinter. The resulting products have included gold, arsenic and antimony. Although not in economical quantities, this deposit is the only epithermal gold deposit to have been found in the UK.

Trewin, N. H. (ed.) 2002. The Geology of Scotland. The Geological Society, London.

Gould, D. 1997. Geology of the Country Around Inverurie and Alford. British Geological Survey (Her Majesty's Stationery Office, London).

Stephenson, D. & Gould, D. 1995. British Regional Geology. The Grampian Highlands. 4th edn. British Geological Survey (Her Majesty's Stationery Office, London).