 |
|||
 |
MINERALS
From the Permian period onwards, the cracks in the limestone became filled with a hot liquid which crystallised to form minerals. It is thought possible that volcanic action inside the earth caused the formation and heating of these liquids, or another idea is that they came somehow from the surrounding sea water.
The veins of minerals (usually called rakes in Derbyshire) all show a similar pattern of bands of different minerals. Galena (lead ore) and/or sphalerite (zinc ore) are in the centre of the vein, with barite and/or fluorite on either side and calcite next to the limestone.
| Lead which is obtained from galena, has been mined in Derbyshire since Roman times or even before. It was used for water pipes, gutters and on roofs. The lead mining industry reached its height in the 18th century when there were thousands of lead mines in the Peak District. Lead mining stopped towards the end of the 19th century, although there are still many remains of the old lead mining industry. |  |
|
|
A Lead Rake |
 |
 |
 |
|
Fluorite
|
Galena and Barites | Calcite |
Fluorite is used in the chemical industry, the iron and steel industry and other applications. (One of these is the ‘fluoride’ in your toothpaste). Most British fluorite is mined in the Peak District.
Barites is used in paint and paper manufacture, and to lubricate the drills on oil rigs.
Calcite is used in the chemical industry, for the white lines on roads and for ornamental finishes to buildings.
 |
|
Blue John Stone
|
A special form of fluorite is mined at Castleton. It is called Blue John which comes from the French words for the two main colours in the mineral - bleu (blue) and jaune (yellow). Many shops in Castleton sell jewellery made from Blue John.
Impure limestone was the basis of the Black Marble industry at Ashford and Bakewell. Fireplaces and tables made from this marble were inlaid with many different minerals and fossils.
SHAPING THE LANDSCAPE
In Permian times, fine sands blew across the dry landscape and some was trapped in hollows in the limestone forming pockets of silica sand, the basis of a local firebrick industry at Friden.
Erosion over many millions of years continued to remove the layers of younger rocks deposited over the uplifted land in the Peak District.
It was the alternating warm and cold periods of at least four ice ages during the last two million years that finally gave the landscape the shape that we now see. Much of the land was frozen during the ice ages. A layer of boulder clay was left in some areas (west of Bakewell) This was formed from the rocks and debris trapped under the ice of the glaciers in the early ice ages. Fast flowing rivers fed by melting ice in the warm periods formed and deepened the valleys. As the rivers became deeper and wider the dales of the present landscape were carved out of the limestone. Some dales were formed, as caverns in the limestone collapsed. Only a few of the limestone dales now have streams because the water has gone underground. Cracks in the limestone widened into caves, as the land froze and thawed. In some places, limey water coming to the surface produce tufa, a honeycombed rock.
A layer of fine sands and silt - called Loess - was blown from the north on top of the limestone plateau in some places.
The final layers of the younger rocks were carried away by erosion during the ice ages, leaving exposed the rocks of the Carboniferous period:- limestone, gritstone and shale.
|
|
||||
 |
||||
|
||||
| POINTS TO CONSIDER | ||||
|
|
||||