Geological Gems

Rocks spanning an incredible 150 million years can all be identified beside the road from Llangadog to Brynaman.


The rock Quarried on the Black Mountain is mostly limestone.

Limestone is made from the remains of millions upon millions of tiny sea creatures that sank to the bottom of a shallow tropical sea when they died just over 300 million years ago, sea when Britain was on the equator! If you look carefully you may discover the fossil remains of some of these creatures in the limestone.

To the north is the Old Red Sandstone and to the south, gritstones and the Coal Measures. Because of its interesting geology, Herbert's Quarry and the surrounding area are included within the Fforest Fawr Geopark. You can learn more about the Fforest Fawr Geopark at

In addition to limestone, other types of rock and mineral resources that outcrop in the surrounding area have also been exploited for a variety of purposes. Silica was used in the manufacture of fire- bricks in the iron industry.

'Rottenstone' was used for polishing copper and tinplate. Related forms of rottenstone have also been used for sharpening blades.


Coal from the south side of the Black Mountain was first mined on a small scale for domestic use and to fuel the limekilns. But in 1838 new developments in the iron industry meant that the anthracite coal of this region could be used in iron furnaces.


Ironstone from Craig Cwm Twrch near or was worked in the early part of the 19th century at Henllys. The iron ore smelted at Ynyscedwyn and forged at Brecon or Llandyfan.