The witherite, calcite, fluorite, barite, linarite, barytocalcite
and plumbogummite have never been beaten, mimetite from Dry Gill (the variety known as campylite) is unique, and the recent finds of boracite from Boulby mine have set new standards for the species.
In general, the sources of barium in groundwater can be barium-rich feldspars, plagioclases, micas, apatite, baryte, barium-carbonate minerals of the aragonite group, such as witherite and alstonite (= bromlite, barytocalcite
), barium rare-earth uranium carbonates, etc.
, hematite, quartz, aragonite, siderite, linarite, caledonite and mimetite.
The mine is the type locality for barytocalcite
(Brooke, 1824), and has yielded some good specimens (lustrous, transparent, prismatic crystals to nearly 1 cm); in fact, it is the only locality in the world where that mineral has been commercially mined.
The original description of alstonite (Johnson, 1835, 1837; Thomson, 1835, 1837; Breithaupt, 1841), which at first was thought to be a form of barytocalcite
, was based on specimens collected from both the Fallowfield mine and the Brownley Hill mine near Alston.
(1837) On the composition of the right rhombic barytocalcite
, the bicalcareo-carbonate of baryta of Dr.
Natrolite in the cavities is overgrown by calcite, fluorite, barytocalcite
, podlesnoite, astrophyllite and, in minor amounts, burbankite, lemmleinite-K and fluorapophyllite.
Metamorphism of the sediments transformed the witherite into sanbornite (with barytocalcite
as a possible intermediate product) but the barite remained unchanged because of its high melting temperature.
Associated minerals are: natrolite, sodalite, aegirine, biotite, vinogradovite, titanite, eudialyte, calcite, barytocalcite
, fluorapatite, fluorite, djerfisherite, and molybdenite.
Associated minerals are: hausmannite, calcite, brucite, dolomite, clino-humite, kinoshitalite, copper, barytocalcite
, bindheimite and cerussite.
The ancient lead mining district of Alston Moor, which lies on the northwestern edge of the North Pennines, has also furnished exceptional examples of two mineralogical rarities: the barium-calcium carbonates alstonite and barytocalcite
(1990) Alsonite and barytocalcite
from Llantrisant, South Wales and Barytocalcite
from Holwell, Mendip Hills, England.