Green fluorite is known to come from three main locations in Weardale - the Rogerley Mine, the Eastgate Cement Quarry, and the Heights Mine and Quarry. Both the Rogerley and the Cement Quarry are relatively recent specimen-producing locations, so it has been generally assumed that any green Weardale fluorite specimen that pre-dates the latter half of the 20th Century came from Heights. As with many assumptions, however, this may not always be a safe one to make. Occasionally, twinned green fluorites that are obviously from the North Pennines, but having some peculiar characteristics can be found in old collections. These characteritics suggest yet another source. Like much Weardale fluorite, these crystals are invariably twinned and show well developed growth lines, or "vicinal faces" on the cube. They also show unusually rounded edges to the cube. The color, while green, is often faded as can happen to green Weardale fluorite over time. These fluorites also appear to have one or more thin purple-colored layers just below the cube face, which become more visible in specimens where the green is faded. What suggests that these specimens are not from the Heights Mine, or any of the other recognized localities for green fluorite in Weardale is that the matrix of these specimens appears to be a friable iron-stained quartz sandstone. All fluorite specimens from the Heights, as well as the Rogerley and the Cement Quarry have come exclusively from the Great Limestone.

A group of green twinned fluorite crystals on a sandstone matrix. The specimen came out of an old German collection, which gave the location as simply "Weardale". A later hand-written note on the reverse of the old label attributed it to the "Frosterley Mine". As there is no mine of that name, perhaps the owner was actually referring to the Rogerley.

A close-up photo of a fluorite crystal on the above specimen showing thin internal purple color zones and rounded edges.

So where do these specimens come from? They are obviously old, as evidenced by the often faded color, numerous old collection numbers glued to the bases, and sometimes old collection labels. The trail of clues begins with "The Strata" by Westgarth Forster, which was published in 1821. This was the first book to document the geology of the Weardale region in a modern scientific context, and Forster's correlation of the regional stratigraphy is still, for the most part, accepted today. In a section where he describes the minerals found in the local lead mines, he states:

"All the extensive mines in Weardale, in the county of Durham, and Allenheads and Coalcleugh, in the county of Northumberland, have calcareous and fluor spars for the matrix; and it is from mines in Weardale, that the beautiful green fluor has been procured lately in such quantities."

Unfortunately, Forster does not say which mine it was that produced the quantities of beautiful green fluor, so we may never know for sure. One thing we do know is that the Heights Mine, regardless of the "matrix problem" can not be the source as it was not in production until around 1850 - much later than the date of Forster's writing. We can, however, engage in the time-honored craft of speculation in the face of insufficent facts. Though mining records from the early 19th Century are rather spotty at best, there is evidence, as cited in both Dunham (1990) and Fairburn (1996), that the lead mines in Middlehope Burn were quite active around the time that Forster was writing. One of these, the Middlehope Shield Mine was accessed by an adit known as White's Level, which was driven below the Great Limestone in a major sandstone unit called the Quarry Hazle. This level accessed the Shield Close, Middlehope Shield, and Middlehope Shield Cross Veins, as well as crossing the Scarsike Vein, which is a southwest extension of the Boltsburn. In addition, judging from their proximity on the map, the Middlehope Shield Cross Vein may be a westward extension of the Heights West Cross Vein.

Another specimen of the "Mystery" green fluorite. The green color of this one has faded and one can see the light purple from a color layer just below the cube face of the crystals. This specimen came labeled as "Heights" but has the sandstone matrix on the base.

Dunham (1990) cites production figures for the time period 1818 to 1864, and Fairburn (1996) states that records suggest the mine was active prior to 1809. The time period and geological setting draw a connection between Forster's reference and the old fluorite specimens on sandstone.

A final piece in the puzzle is found in a publication from the early 19th century. In the “Annals of Philosophy”, vol. XIV, published in 1819 is a short paper by Edward Daniel Clarke, (then Professor of Mineralogy at Cambridge University) entitled “Account of a newly discovered variety of green fluor spar, of uncommon beauty, with remarkable properties of colour and phosphorescence.” In this paper, he describes a large find of “perfectly transparent, intense emerald green” fluorite that occurred at the Middlehope Shield mine, near Westgate, in the autumn of 1818. He goes on to give a description of the specimens that matches quite well those in question, including the crystal twinning, beveled edges, surface “laminae”, and buff-colored, often friable matrix.

A corroboration of this may be found in the Arthur Russell collection, housed in the Natural History Museum, London. In the collection, mixed in with specimens from the Heights mine, are several green fluorites with a sandstone-like matrix. One of these specimens, collection number 1524, was acquired by Russell from a 19th Century collection and is recorded in his ledger as being from White’s Level. Unfortunately, White's Level was never reopened in the 20th century during the region-wide resurgence of mining for fluorspar, so there are no modern descriptions of the mine and its mineral deposits. The level is long collapsed, and the area encompassing much of Middlehope Burn is now a protected archeological site, so it is unlikely that anyone will get there again any time soon to have a look.

The portal of White's Level in June, 2003. This was the main level for the Middlehope Mine, which was active through the first half of the 19th Century.

Middlehope Burn hosts the remains of several of Weardale's more productive 19th Century lead mines, along with some marvelous scenery. To see more, click on the "Tour Middlehope Burn" link below. I would like to thank Lindsay Greenbank for first bringing the "sandstone dilema" to my attention, and to David Green for providing a copy of Mr. Clark's article.

Download a copy of Clark's original article. Required Adobe Acrobat Reader.

---

Go Home

Tour Middlehope Burn