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Sceptered Amethyst from Ashaway Village,

Hopkinton, Rhode Island

The eastern United States is well known for its many occurrences of exceptionally well formed amethyst specimens. In the spring of 1981, an occurrence of amethyst scepter overgrowths on milky quartz was discovered in Ashaway Village, Hopkinton, Rhode Island. This deposit has produced some of the most beautiful amethyst specimens found in the Piedmont of the eastern United States.

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The amethyst specimens occur in broken up quartz veins, each approximately 36 cm thick. No surface exposure of these quartz veins has been found and they have only been accessible where small temporary pits were dug during excavation. Hence, little field data regarding the relationship of the veins to the regional geology are available.	Diamond Hill is formed on the western limb of a north-south trending syncline with displacement along a major fault that cuts across the southwestern corner of Rhode Island. The quartz lies stratigraphically above a lithologically variable quartzite unit of the Proterozoic-aged Plainfield Formation and is, in turn, overlain by 0.6 to 1.6 meters of glacial till.

Three varieties and several different habits of quartz crystals are present. Optically clear quartz occurs as elongate, pencil like, euhedral crystals with a length to width ratio of 6:1 or greater. These commonly occur in tightly packed groups of crystals in parallel growth. The transparent quartz also occurs as short prismatic crystals that commonly are flattened perpendicular to {1010}. Frequently these crystals have one well developed {1121} face.

Quartz. The crystal measures 2.6 x 15.25 cm

Euhedral milky quartz is the most abundant variety found. The crystals typically are uniform and prismatic with development of {1010}, {1011} and {0111} only. These crystals have a clear core and a thinner concentric rim of alternating clear and milky layers. The opaque, milky layers result from increased fluid inclusion concentrations in the quartz.

Amethyst is the third variety of quartz that occurs at this site. Almost always, the amethyst occurs as "scepters" or epitaxial overgrowths on the milky quartz. These overgrowths are equant in habit, with the base of the amethyst overgrowth terminated and forming a reentrant with the euhedral stem. This overgrowth produces a scepter with a mushroom like appearance.

Some of the finest specimens recovered are on display at the National Museum of Natural History in Washington, the American Museum of Natural History in New York, and the Harvard Mineralogical Museum in Cambridge. The amethyst is usually fairly transparent, with color ranging from faint violet to a deep purple. The amethyst is commonly sector zoned with respect to color.
	Amethyst on milky quartz. The specimen measures 12.7 x 25.5 x 30.5 cm, and the largest scepter is 2.5 cm across.


Sal Avella and John Rakovan, discussing where to dig next.

dD-d18O plot showing isotopic compositions and fields for Hopkinton quartz fluid inclusions, primary magmatic waters, metamorphic waters, and standard mean ocean water (SMOW). The line across the upper left part of the graph is the compositional line for meteoric waters. Contrary to initial speculations, the geochemical evidence demonstrates that the quartz is not related to an igneous source, but rather precipitated from meteoric waters during several stages of precipitation.

Amethyst on milky quartz. The scepter measures 3.8 x 5.5 cm.

John Rakovan photo


Amethyst on milky quartz. Specimen measures 8 x 10 x 10 cm, and the largest scepter is 2.5 cm wide. John Rakovan photo.	Amethyst on milky quartz . The specimen measures 10 x 9.5 x 12.5 cm and the scepter is 6.5 cm long. John Rakovan photo

Amethyst on milky quartz. Specimen measures 9 x 6.5 cm.

John Rakovan photo


Amethyst on milky quartz. Specimen measures 10 cm long. John Rakovan photo.	Same amethyst on milky quartz . The specimen measures 6 cm wide. John Rakovan photo