Fred Parker Updates his 2005 Hunting Hill Mineralogical Record Article

by Fred Parker. 

This  is an update on minerals uncovered at Montgomery County Maryland's Hunting Hill Quarry since my 2005 article in The Mineralogical Record, Vol.36, Sept.-Oct., 2005, pages 435-446. That article recorded 60 different mineral species known to occur at the quarry.

The quarry rewarded collectors with an additional 15 species in the five years subsequent to this article . Since 2010, however, the ownership has strictly prohibited all collecting. It has given no reason to believe that any kind of mineral collecting will be permitted in the foreseeable future.

The mineral descriptions below note the 15  mineral species uncovered between late 2005 and when the collecting ended in 2010. Substantial variation in the types of  these species  further illustrates the complexity and unique mineralogy of this unusual serpentinite/rodingite locality.

Sadly, the scientific and collecting communities are now denied scientific and mineralogical knowledge. The reasons relate to mining regulations and liability insurance issues.

The 15 additional species are as follows:      

• Albite-Anorthite: Seams containing opaque white well-formed feldspar crystals were collected by Erich Grundel in 2006. He exposed the crystals by dissolving calcite infilling of feldspar pockets. Composition was determined to be intermediate in the Albite -Anorthite series. (Personal communication - Erich Grundel.)

• Brochantite: Dark green coatings on serpentine (Jon Ertman, personal communication.)

• Chabazite: Locally found as crusts of colorless to white glassy rhombohedra to 2 mm. lining seams in serpentine. (XRD confirmation by Lance Kearns.) 

• Erythrite: Pink Coatings on a talc vein (Personal ommunication from Jake Slagle. Ex-Jay Lininger Collection. 

• Heulandite: Locally found as crusts of pearly "coffin-shaped" crystals in narrow fractures in serpentine. Color ranges from tan to white. Crystal reach a maximum size of 3 mm. (XRD confirmation by Lance Kearns).

• Laumontite: (leonhardite): locally found with minute(1-2 mm) white acicular crystals associated with other zeolites. (visual identification)

• Margarite: Pale green scaly in serpentine (reported by numerous collectors). 

• Mesolite: From a single occurrence in 2007: White silky radiating hemispheres and crusts to 1 cm. associated with an unusual orange-yellow prehnite (XRD confirmation by Lance Kearns).The silky texture and radiating structure distinguish mesolite from the more common scolecite. 

• Nacrite: Very fine-grained coatings on rhombic cleavage plane of calcite; after acid etching of the calcite, nacrite formed fragile rhombic structures mimicking the dissolved rhombic calcite. (Dave Hennessy, personal communication.

• Pecoraite: Very fine green pwodery coatings on millerite needles (visual identification)

• Scolecite: Pockets in serpentine were locally lined with abundant elongated white bladed crystals to 8 mm. Confirmation by XRD and EDS by Lance Kearns. 

• Stellerite: Repeatedly found as white, sheaf-like crystals to 5 mm. coating cavities in serpentine with calcite. (George Reimherr personal communication.)---Stellerite is the greenish crystalline crust in the image image where laumontite was noted. 

Acknowledgements: The mineral identifications cited throughout this update would not have been possible without the support and analytical determinations provided by Dr. Lance Kearns of James Madison University, Harrisonburg, VA. His contributions to regional mineralogy are greatly appreciated by the mineral collecting community.