Foster's Hush is a Site of Special Scientific Interest

Site of Special Scientific Interest

A Site of Special Scientific Interest is a conservation designation denoting a protected area in the United Kingdom. SSSIs are the basic building block of site-based nature conservation legislation and most other legal nature/geological conservation designations in Great Britain are based upon...

 in the Teesdale

Teesdale (district)

Teesdale was, from 1974 to 2009, a local government district in County Durham, England. Its council was based in Barnard Castle and it was named after the valley of the River Tees....

 district of west County Durham

County Durham

County Durham is a ceremonial county and unitary district in north east England. The county town is Durham. The largest settlement in the ceremonial county is the town of Darlington...

, England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

. It is located in the valley of Lune Head Beck, immediately south of the B6276 road, 6 km upstream of the Selset Reservoir

Selset Reservoir

Selset Reservoir is a reservoir in County Durham, England. It is situated in the Lune Valley which is a side valley of the River Tees, about 5 miles west of Middleton-in-Teesdale. It supplies water for Teesdale and is owned by Northumbrian Water. It was built in 1960 and its main use is...

 dam.

At Foster's Hush, workings of a mineral-rich vein

Vein

In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...

 in the Great Limestone and Tuft Sandstone have exposed mineralisation of a rare mineral, witherite

Witherite

Witherite is a barium carbonate mineral, BaCO3, in the aragonite group. Witherite crystallizes in the orthorhombic system and virtually always is twinned. The mineral is colorless, milky white, grey, pale yellow, green, to pale brown. The specific gravity is 4.3, which is high for a translucent...

. The site has been listed by the Geological Conservation Review

Geological Conservation Review

The Geological Conservation Review is produced by the UK's Joint Nature Conservation Committee and is designed to identify those sites of national and international importance needed to show all the key scientific elements of the geological and geomorphological features of Britain...

, both for the excellent mineral specimens it has provided and because it is the only locality in the North Pennines

North Pennines

The North Pennines is the northernmost section of the Pennine range of hills which runs north-south through northern England. It lies between Carlisle to the west and Darlington to the east...

 ore-field where witherite mineralisation can be observed in situ at the surface.