Introduction: gypsum is a common sulphate mineral typically formed as an evaporite mineral particularly by the evaporation of lakes in arid regions. Gypsum also forms as thin bladed crystals on the walls of caves and mines as the variety selenite.

Occurrence in Wales: in Wales gypsum occurs in a wide range of geological settings and in a variety of forms. In South Wales, massive gypsum known as alabaster forms nodules and beds of nodules in the undivided ‘red mudstones’ and the Blue Anchor Formation of the Mercia Mudstone Group of Triassic age exposed in the Penarth-Barry area (North, 1916; Waters & Lawrence, 1987; Bevins, 1994). Veins of fibrous ‘satin spar’ also occur, particularly within the ‘red mudstones’ as witnessed in coastal cliffs between Penarth and Lavernock. Crystallized gypsum is quite common in caves and within disused mine workings, where it precipitates as the variety selenite. Crystals are typically colourless to creamy orange, translucent to transparent and usually very brittle. Good examples have been found in a number of Carboniferous Limestone caves in South Wales and within acidic mine workings, including Britannia Mine on Snowdon, Cae Coch Mine, near Trefriw and Castell Carndochan Mine, near Bala, all in North Wales.

Last saved full search

Alphabetical search:

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z