£1.00 – £2.74
Tuff from the Borrowdale Volcanic Group, Ordovician in age, the rock has a green colouration to it and a slate like cleavage, hence sometimes being known as volcanic slate, green slate or Borrowdale slate. Rock specimens are available in 3 optional sizes and will come supplied in a card tray with a label.
Volcanic tuff is an igenous rock, more specifically, belonging to the pyroclastic group. Pyroclastic rocks are essentially composed almost all from volcanic material although sometimes, inclusions of country rock (the surrounding rock which was already in place) can be seen. Volcanic tuff is formed from phreatomagmatic eruptions, where volcanic material such as ash and pyroclastic bombs are ejected from the volcano during eruptions. Tuff is essentially derived from the ash which has been ejected out of the volcano during activity, originally a fine grained ash, as the ash settled, over time through various geological processes, the ash consolidates into a solid rock which geologists know as tuff. This particular variant of tuff is green in colour due to the presence of chlorite, this particular tuff also has a slatey cleavage, meaning it breaks in slabs or slices, very similar to slate and is in fact also known as Borrowdale slate, green slate or volcanic slate. It comes from the Borrowdale valley in Cumbria, an area rich in volcanic history, the valley itsself is actually named after the Borrowdale Volcanic Group, which is comprised of a series of various volcanic rocks which formed during the Ordovician period. Specimens are available in various optional sizes and come in a card tray with a label.