MINERALOGICALMINERALOGICALMAGAZINE,SEPTEMBER

Alstonite in situ at Brownley Hill
Mine, Nenthead, Cumbria
Tnz mineral which eventually came to be known asalstonite was originally described by Johnston (1835,1837) and Thomson (1835) from specimens obtained
from both Brownley Hill Mine, near Alston, Cumbria[NY 776 446] and Fallowfield Mine, near Hexham,
Northumberland [NY 938 677]. In these originaldescriptions the mineral was regarded as a form of barytocalcite which had been described as a new mineralby Brooke (1824). The separate identity of the BrownleyHill mineral was recognized by Thomson (1837) whoproposed the name 'bromtite'. This name appears tohave originated from a mis-spelling of the locality as'Bromley Hill'. Four years later Breithaupt (1841) introduced the name 'alstonite', which became the acceptedname for the species despite the apparent priority ofThomson's 'bromfite'.
Although Brownley Hill Mine is thus the type locality
for alstonite no details of its occurrence here have everbeen published, though according to Walton (pers.
comm. in Spencer, 1910, p. 304) the original specimens
were obtained from Jug Vein. Dunham (1948, p. 171)
noted the presence of barium carbonates, including
alstonite, in the north eastern workings of the mine.
In a recent review of barytocalcite and alstonite occurrences in the northern Pennines, Young (1985) commented on the presence of alstonite at four localities,
including Brownley Hill, though no detailed information on the occurrence at the type locality was given.
Beautifully crystallized specimens of alstonite are to
be seen in many collections of British minerals. In mostexamples we have examined, the mineral forms whiteto colourless acute pseudohexagonal pyramids or bi-pyramids up to 6 mm long. In some specimens the alstonite
is intergrown with very thin hexagonal platy crystalsof 'nail head' calcite. In very many instances the alstonite encrusts compact crystalline white to pale pinkbaryte. Surviving acquisition details of Brownley Hill
alstonite specimens suggest that they must have beencollected in the mid years of last century, presumably
shortly after the mineral's original description. Nall
(1888) noted that the workings of Brownley Hill Mine
which yielded alstonite had for some time been supposed to be inaccessible. Apparently the mineral wasvery highly prized by collectors of the day as Nail (loccir.) further commented that even small specimens werethen fetching as much as five pounds.
Some years ago parts of the workings at Brownley
Hill could still be examined though these are now inaccessible. Underground investigation revealed extensive

NOTES
1990, V O L . 54, P P . 515-516

workings in Jug, West High Cross and High Cross Veinsin the Great Limestone (Namurian), as noted by Dunham (1948). Mineralization remaining in unworked portions of the veins and on the walls of old stopes,
suggested that the main minerals present, in addition
to the ore minerals galena and sphalerite, are ankeritewith smaller amounts of quartz, calcite, pyrite andlocally baryte.
In view of Walton's comments (pets. comm. inSpencer, 1910) on the source of the original alstonite
specimens, particular attention was paid to the Jug Vein
workings. This vein was found to be up to 2 m wide:
minerals present in the remaining veinstuff Were foundto be ankerite, quartz, galena and sphalerite. No traceof baryte or of any barium carbonate mineral was found.
Extensive workings on High Cross Vein revealed that
it was up to 2 m wide. Ankerite and quartz are again
the major gangue minerals. These are accompanied
locally by pockets of coarsely crystalline white to very
pale pink baryte and a little white calcite. High Cross
Vein was well exposed in a stope in the Great Limestone
above the Horse Level between Holme's Rise andRichardson's Rise. The vein is here almost vertical witha downthrow to the west of about 0.3 m and is up to2 m wide. Over much of the approximately 60 m ofaccessible strike length of this stope the vein was seen
to be composed mainly of broken limestone in which
occur vertical bands of galena up to 10 mm wide. Theeast, or hangingwall, side is marked by a band of intergrown galena and ankerite up to 100 mm wide. Pink
to white, compact crystalline baryte with, locally, somecoarsely crystalline calcite, and small amounts of pyrite
and galena, form a band up to 120 mm wide on thewest or footwall. Towards the southern end of the stope
several vugs in this baryte, elongated parallel to thevein walls, contain well developed alstonite crystals. In
general these vugs are up to 50 mm across and 70 mm
long but one spectacular vug up to 1.5 m long and 0.3
m wide was exposed near the floor of the stope.
It is clear that in the past many specimens have beencollected from these vugs and several good examples
of alstonite were obtained during the investigation.
These exhibit the characteristic morphology of acutepseudohexagonal pyramids or more rarely bi-pyramids
up to 5 mm long, the faces of which typically show prominent horizontal striations with a vertical medial reentrant line. The identity of the alstonite was confirmed
by X-ray diffraction (Ph 7475)*. The alstonite crystals
commonly grow on coarsely crystalline baryte andlocally ankerite (Ph 7476): in some specimens they growon, and are intergrown with, large white crystals o[ 'nail* BGS X-ray number

516

MINERALOGICAL

head' calcite. Examination of one sample of this calcite
by X-ray diffraction revealed the presence of traces ofbarytocalcite (Ph 7474). Despite careful search of thisand other specimens, barytocalcite has not been foundseparately on any of the alstonite-bearing samples.
Insufficient material was available to investigate further
the relationship of this barytocalcite to the associatedminerals. Well crystallized barytocalcite was recorded
by Young (1985) from the dumps of Brownley Hill Minethough the provenance of the mineral within the mine
could not be established. In these specimens the only
associated mineral is a little scalenohedral calcite: noalstonite was found. The dump specimens are unlike
anything seen in the extensive workings during thisinvestigation.
Almost all of the alstonite-bearing specimens
obtained during this investigation bear a striking
resemblance, both in morphology and paragenesis, tospecimens of alstonite collected from Brownley Hill
Mine last century. It is thus very likely that at least
some of these early specimens were obtained from High
Cross Vein. Jug Vein cannot be ruled out as a former
source of alstonite specimens though it is noteworthy
that no trace of barium minerals has been found in it.
Both alstonite and barytocalcite occur locally within
the veins formerly worked at Brownley Hill though it
has not been possible to establish the relationship ofthe minerals one to another.

Acknowledgements.. We thank Mr Atkinson, M. Suttcliffe, R. Phillips and M. Wood all of whom provided
essential help in the field investigations. This note is
published with the approval of the Director, British
Geological Survey (NERC).

NOTES

Brooke, H. J. (1824)Ann. Phil. 8, 114-6.
Dunham, K. C. (1948) Thegeology of the Northern Pennine Orefield: Volume 1, Tyne to Stainmore. Mem.
Geol. Surv. Great Britain.
Johnston, J. F. W. (1835) Phil. Mag. 6, 1-4.
-(1837) Ibid. 10, 373-6.
Nail, W. (1888) A handbook to Alston. The Wordsworth
Press, Carlisle.
Spencer, L. J. (1910) Mineral. Mag. 15, 302-11.
Thomson, T. (1835) Rec. Gen. Sci. 1,369-75.
-(1837) Phil. Mag. l l , 45-8.
Young, B. (1985) Proc. Yorkshire Geol. Soc. 45,
199 206.

KEYWORDS." alstonite, B r o w n l e y Hill M i n e ,Cumbria.
B. YOUNG

British Geological Survey, Windsor Court, Windsor
Terrace, Newcastle upon Tyne NE2 4HB
L. GREENBANK'Birchfield', 16 Sedbergh Road, Kendal, Cumbria
LA9 6ADP. H. A, NANCARROW

British Geological Survey, Keyworth, Nottingham
NG12 5GG

References
Breithaupt, A. (1841) Holoedrites syntheticus oder
Alstonit, Br. In Vollstand. Handb. mineral. Dresden/Leipzig, 225-56.

[Manuscript received 20 October 1989;
revised 20 December 1989]
9 Copyright the Mineralogical Society