Another wonderful book on a classic New York State mineral location is available. Many of us have ventured to the Bower Powers Farm in Pierrepont to collect black tourmaline. We have driven Post Road to the washed out bridge over Leonard Brook, hiked along the brook to the tourmaline laden pits, and collected what we could carry. But did you ever want to know more about the rich history of the location, the multiple collecting sites, the varied geology, or the complete mineralogy of this classic site?
This article was published in the November issue of Wayne County Gem and Mineral Club News. Ninety-one dravites from the WCGMC collection were used to wish the members Happy Halloween.
Dravite is a tourmaline within the Alkali Subgroup 1. This means that the X-site in the complex formula below is predominantly occupied by sodium (Na). In the case of dravite the Y site is occupied by magnesium (Mg) and the Z site is aluminum (Al). The boron cyclosilicate mineral is always dark in color, ranging from chocolate brown to almost jet black. Occasionally, there is sufficient chromium in the Y and/or Z site to impart a dark green color. Dravite is most commonly found in metamorphosed limestones and in higher grade mafic schists.
Article I wrote for the June-July, 2014 WCGMC News
SELLECK ROAD, POWERS FARM
On June 21-22, the WCGMC returned to St. Lawrence County for more mineral fun. Green growth now obscured the rocks a bit and mosquitoes and black flies greeted the 19 club members who arrived at Selleck Road in Pierrepont on Saturday morning. The two day trip would also include the Powers Farm and two sites where Pierrepont ZCA zinc ore has been stockpiled for road use (or perhaps for collectors?).
An article I wrote for the April, 2014 WCGMC News (www.wcgmc.org)
ALL TOURMALINES ARE NOT CREATED EQUAL
When we venture to Ace of Diamonds to dig clear quartz crystals we are seeking a very simple mineral, silicon dioxide (SiO2). Just simple SiO4 tetrahedrons joined together with each large oxygen atom shared by two small silica atoms in a six-sided prism, ideally terminated by 6-sided pyramids. And when we seek that elusive fluorite at the annual Walworth Quarry dig, it is just calcium and fluorine combined into a cubic lattice motif with Ca atoms centrally located and F at the corners. This time each of the 8 fluorine corner cube atoms are shared by four unit cells with the formula CaF2. In both minerals inclusions generate color variations which get neat names (like amethyst or citrine). Of course, quartz can twin or show spectre form, but there is no elemental substitutions of note into the lattice of either mineral, and there are no solid solutions to confuse collectors: just simple SiO2 or CaF2, just quartz and fluorite.
It is not as simple with tourmaline. When we travel north to St. Lawrence County to collect dravite at Powers Farm, or fluor-uvite at Bush Farm or Selleck Road we are focusing our attention on one of the most complex mineral structures known. The mineral lattice of tourmaline actually has five structural sites where elements can be swapped and traded, six if you count the rare substitutions of aluminum or boron into the Si site. These substitutions can be complete or partial, and often occur in zonal patterns such that the center of the crystals actually may qualify as distinct minerals from their outside layers.
The compositional variety, the range of color variation, and the diverse origin of tourmalines has led to several books on the subject. Some are very technical, either mineralogically or technically, but for me one stands out for the mineral collector. The Collector’s Guide to the Tourmaline Group by Robert J. Lauf (Schiffer Publishing) combines adequate detail on tourmaline chemistry and taxonomy with a pictorial account of all the recognized tourmaline species. Lauf does all this at a level that is not daunting for the non-geologist. The price is right also, $19.99 list for the oversize softcover book, and I found it for a few dollars less online.
Incidentally, this is one of a series of books published by Schiffer on various minerals or mineral groups. All are informative and affordable and well illustrated.
Occupying an east-west ridge just south and parallel to Selleck Road in West Pierrepont this location has been collected for decades. The main part of the ridge is on state land and accessible without much walking, thereby adding to the popularity of the site. Tremolite is everywhere, tourmaline (v. uvite) is much more localized along the ridge. Both the light green tremolite and the uvite is typically etched and non-gemmy, however isolated pockets of very gemmy material has been found.