Jail Hill Road locality (Jail Hill Quarry), Haddam, Middlesex County, Connecticut, USAi

Regional Level Types
Jail Hill Road locality (Jail Hill Quarry)	- not defined -
Haddam	Town
Middlesex County	County
Connecticut	State
USA	Country

This locality consists of two types of different but adjacent mineral deposits immediately east of Jail Hill Road; a narrow granitic pegmatite and, at its southern terminus, in the surrounding metamorphic rocks, a small manganese-rich deposit.

The pegmatite is a common pegmatite consisting mainly of albite, microcline, and smoky quartz with muscovite, which is typical of the Middletown district according to Stugard (1958). According to the Haddam Historical Society web site, this little pegmatite, situated on grounds belonging to the farms associated with the nearby Middlesex County jail, was discovered in 1914 "and prisoners were employed to quarry the stone which was sold to out of state firms."

According to Seaman and Gallant (1960), the geological occurrence of the Mn-rich deposit is a pod about 1.6 meters in its greatest width. It is enclosed within a quartz-biotite schist that strikes nearly north-south and dips about 75 degrees east to nearly vertical. The mineralogy of the pod is mostly spessartine (confirmed by X-ray diffraction, Raman spectroscopy and SEM-EDS). Along the eastern contact there is a development of massive spessartine with included rhodonite and radiated actinolite. Schooner (1961) describes the variation in spessartine here, "The color of the spessartite ranges from dark red to orange-red to yellowish-orange, with the intermediate shade predominating. Big specimens were obtained, showing virtually pure garnet; the material is very solid and unfractured". Apparently this spessartine-rich rock was first reported by Williams (circa 1945): "In a field and along the road large masses of Garnet occur in Syenite-Gneiss, near the N. Spencer house." That house corresponds to the one present just to the south of the quarry.

Schooner (1961) reports apatite as small white prisms.

The identity of the granular pink mineral(s) has been difficult to pin down. Schooner (1961) says, "rhodonite is found in irregular cleavage masses up to two inches across, embedded in massive spessartite, with some actinolite, calcite, and quartz. The rhodonite is of an attractive pink color, though stained in many places by a manganese dioxide mineral; brown and green materials, perhaps rarer manganese silicates, are associated in some specimens." Later, however, Schooner reported that the Mn-rich deposit was studied by the University of Michigan and USGS, which did numerous X-ray diffraction identifications. They changed the "rhodonite" to bustamite and pyroxmangite (a polymorph of rhodonite) and many other Mn minerals were identified. Schooner alludes to this research in his circa 1990 unpublished manuscript on central Connecticut mineralogy. However, a 2014 Raman spectroscopic analysis of a fine-grained pink mass, initially identified as rhodonite by Charles and Marcelle Weber, confirmed its ID as rhodonite. SEM-EDS analyses done in 2019 by Micromounters New England on several specimens posted here did not identify any pink grains as bustamite, but only as rhodonite/pyroxmangite polymorphs and one as rhodochrosite. All four minerals could be present. Some brown granular specimens labeled as tephroite proved to be spessartine, but one has a darker brown area that is tephroite.

As of 2006, massive spessartine and tiny crystals in quartz could still be found there.

Other Regions, Features and Areas containing this locality

References