However, a series of larger nodules up to about 1 meter in diameter, found at or near the base of the Boulby Potash in the north and west of the mine, have furnished most of the line boracite specimens collected in the 1990s.
This is not a distinct mineral species; analyses showed its composition to be borderline between boracite and trembathite.
At the Boulby mine, boracite occurs within massive sylvinite ore in a variety of habits ranging from isolated single crystals to large nodules.
Examination of the boracite nodules suggests that some are formed by aggregation of spherules a few millimeters in diameter.
It is the type locality for povondraite and magnesioriebeckite, and has also produced abundant sharply-formed, doubly-terminated danburite crystals, the world's largest boracite
crystals, and interesting specimens of ericaite, dolomite, magnesite, and several other species.
The mine has recently been reported in mineralogical journals as a new locality for well-crystallized boracite and hilgardite (Robinson and King, 1993; Cooper, 1994; Moore, 1994; Weiss, 1994).
Most of the unusual species described below, including anhydrite, boracite, ericaite, hilgardite, magnesite, rectorite and syngenite were identified by X-ray powder diffraction at Manchester University.
Anhydrite occurs very rarely within boracite nodules as poorly developed, pale lilac, translucent, equant to prismatic crystals.
This is not a distinct mineral species; analyses show its composition to be borderline between boracite and ericaite.
The Boulby mine, Loftus, Cleaveland, Yorkshire, has continued to produce more of the remarkable pale blue-green boracite
He introduced powdered boracite
into the blowpipe flame and it showed a typical green color.
update from England: the Boulby potash mine near Cleveland in Yorkshire is still operating (barely) and the general quality of these lovely pale green sparkling boracite
druses is up from the time of the last Denver Show.