It is famous for producing the world's finest specimens of blue boracite, as well as trembathite and hilgardite.
Thicker but less perfect crystals are sometimes revealed when the central core of sylvite present in some of the hilgardite nodules is dissolved.
Relationship to other species: Related to hilgardite, [Ca.
Comments: The mineral was originally described by Yarzhemskiy in 1952 but was discredited by von Hodenberg and Kuhn in 1982 as "strontium hilgardite.
The Boulby potash mine has produced some of the world's finest specimens of blue boracite, ericaite and hilgardite.
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.
This was shown to be identical to the "tri-clinic" hilgardite of Rumanova et al.
Evaporite rocks at the Boulby mine have provided a suite of minerals, including some of the finest known examples of the borate minerals ericaite, boracite and hilgardite.