Minerals and mines

Introduction

There has been a long history of mining on the Mendip Hills stretching back over 2000 years to Iron Age times.

Many minerals have been won from the region, but the most common were the ores of lead, zinc and iron. It has been estimated that about 100 000 tons of lead have been obtained from the Mendips. Small amounts of manganese, silver (associated with lead ore), barium and strontium have also been worked. In East Mendip, there are relatively few mineral deposits, but here coal mining was once an important industry.

There must be literally thousands of mines scattered across the Mendip Hills, most of which remain unexplored. Most of the known mines are small, up to 40 m deep and generally less than 100 m long, but a few of the larger mines have several hundred metres of passage. Not all the mines produced ore, many were exploratory shafts sunk along calcite veins in the hope of fining richer ore bodies.

Most of the lead ore came from the central Mendip region between Charterhouse and Green Ore, whereas most of the zinc was obtained from the region around Shipham and Rowberrow. Smaller ore fields occurred as far afield as Banwell and Shepton Mallet. The region was divided into four mining districts known as ‘liberties’ at Priddy, Chewton, Charterhouse and Harptree. Today, there are no active mines. Instead, the most valuable mineral is the rock itself.

Gangue minerals
Calcite	CaCO₃	A very common mineral the main constituent of limestone.
Aragonite	CaCO₃	A polymorph * of calcite
Dolomite	(MgCa)CO₃	A common sedimentary rock-forming mineral, the main constituent of the rock dolomite
Barytes	BaSO₄	A common, heavy, yellow mineral
Lead minerals
Galena	PbS	A distinctive heavy, shiny, lead ore.
Cerrusite	PbCO₃	A secondary white, lead carbonate mineral, formed by alteration or weathering of a primary mineral
Pyromorphite	Pb₅(PO₄,AsO₄)₃,Cl	A green lead ore occasionally found on Mendip
Zinc minerals
Sphalerite	ZnS	A grey metallic zinc sulphide mineral
Smithsonite	ZnCO₃	A secondary mineral and the main zinc ore, formed by alteration or weathering of a primary mineral.
Iron minerals
Goethite	FeO,OH	A complex dirty iron ore
Haematite	Fe₂O₃	Common iron ore, blood red when powdered
Limonite	FeO,OH	A mixture or iron oxide minerals
Ochre	FeO,OH	A mixture or iron oxide minerals
Iron pyrite	FeS₂	Also known as fool's gold
Manganese minerals
Pyrolusite	MnO₂	Also known as Wad
* A polymorph is a mineral with the same chemistry as another material, but with a different structure, and more importantly, different symmetry and crystal shapes.

Table of common minerals found on Mendip.