Walden Gem Quarry, Portland, Middlesex Co., Connecticut, USA

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A lithium rich granite pegmatite opened for specimen and gem mining in 1962. It is not the same locality as the nearby Gotta-Walden prospect, which is a mica, feldspar, beryl prospect operated before and during the early 1940s. The quarry was opened up early in 1962 by two young miners who leased the property from Mr. Walden. The ledge had never been previously blasted but outcropped prominently on top of the hill.

Seaman (1963) describes the pegmatite as follows:

"The Walden quarry is located in a lenticular body of pegmatite. It is a zoned pegmatite and the contact with the schist is sharp; the other contact at the time of the writer’s visit being hidden. The border zone is only a few inches thick and consists chiefly of granular albite, muscovite, and quartz. The wall zone consists of intergrown albite of the variety cleavelandite, quartz, muscovite, biotite [annite], black tourmaline, a few small black columbite crystals, pale yellow to light green and colorless beryl crystals, and frequently large crystals of almandite-spessartite garnet. It grades into a rich lithium mineral zone in the core of the pegmatite. The minerals of the core zone are highly colored lithium tourmalines with the pink or rubellite being the most prevalent color, also light green, dark blue, and a small amount of pale watermelon colored tourmaline; massive and fine grained purple lepidolite; some wedge shaped, hemispherical grown, purple lepidolite; white, gray, and pale blue albite of the variety cleavelandite; spodumene; pollucite; caesium beryl, both morganite and goshenite; montebrasite; mangantantalite; yellow microlite and dark brown pyrochlore; rare, dark blue manganapatite; and granular to massive clear, and smoky quartz.
Parts of the spodumene contain clear, purple areas of gem kunzite from which small stones could be cut. Some of the caesium beryl contains transparent areas of both morganite (pink) and goshenite (colorless) material suitable for fashioning into gem stones. A few of the pink tourmalines also possess small, clear, gem areas."

Barton and Goldsmith (1968) give this description, with corrections in [ ]:

"At the surface the western pegmatite has a maximum thickness of 10 feet, the eastern one, 20 feet. Both pegmatites thin rapidly in both directions along strike, the upper (western one) splitting into three branches before it pinches out to the south. The eastern and larger pegmatite consists mostly of [microcline] perthite crystals up to 1 foot in diameter separated by veinlets and pods of smoky and lesser amounts of milky quartz, usually with less than 6 inches between the feldspar crystals. Scattered books of muscovite average 1 inch across by 1/2 inch thick. Light green to yellow beryl crystals up to 1 foot long by 6 inches thick comprise 0.1 percent of the rock. There is very sparse accessory garnet and biotite [annite]. A 6-inch-thick wall zone along the exposed hanging wall consists of a finer grained mixture of feldspar and quartz with small green, beryl crystals com¬posing 1.0 percent of its constituents. The very fine grained border zone is less than 1 inch thick and consists of biotite [annite] and smoky to citrine quartz. The smaller, western pegmatite is rich in alkalis and is the one from which the gem stones are recovered. It is similar mineralogically to the Dunton pegmatite at Newry Hill, Maine. The exposed pegmatite is principally cleavelandite. The outermost 3 to 5 feet is enriched in almandite garnet and black tourmaline and cleavelandite is white rather than gray to blueish-green, but this color change may be a result of near surface leaching. Gray quartz and a small amount of perthite are associated with the cleavelandite in this zone. Muscovite is sparse and in small books only. The inner zone of colored cleavelandite actually is more a series of replacement pods rather than a true zone. Both downdip and along strike it grades into perthite-bearing pegmatite similar to the eastern pegmatite outcrop. The cleavelandite pods in places contained large masses of deep purple lepidolite forming 10 percent of the rock over areas of several cubic feet. Green, white, and pink beryl up to 1 foot by 6 inches formed about 0.5 percent of these areas. Spodumene including gem kunzite and hiddenite was present in logs up to 1 foot by 4 inches comprising about 1.0 percent of the lepidolite enriched areas. Pollucite in masses up to 1 foot across was seen, in similar concentration. Rubellite up to 6 inches long was also closely associated with the lepidolite. Small (1/8-inch) dark red manganotantalite was an abundant accessory in restricted sections a few inches across. Manganoapatite was fairly common and rare minerals present included autunite, columbite, pyrochlore [microlite], amblygonite [montebrasite], and uraninite."

Mineral List

Albite var: Cleavelandite 'Allanite' Almandine Annite Autunite Beryl var: Aquamarine var: Goshenite var: Heliodor var: Morganite 'Biotite' Cassiterite

'Columbite' Columbite-(Fe) Elbaite 'Feldspar Group' Fluorapatite var: Mn-bearing Fluorapatite Gypsum 'Hornblende' Lepidolite Manganite Meta-autunite Microcline Microlite Group

Montebrasite Montmorillonite Muscovite Opal var: Opal-AN Pollucite Pyrolusite Quartz var: Chalcedony Schorl Spessartine Spodumene var: Kunzite

Sulphur Tantalite-(Mn) Topaz 'Tourmaline' 'var: Indicolite' 'var: Rubellite' 'var: Watermelon Tourmaline' Uraninite Uranophane Zircon var: Cyrtolite

50 entries listed. 29 valid minerals. 2 erroneous literature entries.

References