Cumberlandite History

CUMBERLANDITE - The Official State Rock of Rhode Island. This is an extremely rare
and unique stone and has significant historical and geological interest. This very special
rock was originally named Rhodose and was identified hundreds of years ago but was
renamed Cumberlandite by Wadsworth (1861). In 1966 by the Rhode Island General
Assembly because it is extremely rare and unique nature officially adopted as the official
state rock of Rhode Island (Resolution #268). Cumberlandite was formed over 1.5 Billion
years ago when a small volcano erupted and 24 different minerals mixed together with
molten rock and when it cooled formed a slightly magnetic rock that is iron rich. It was
later exposed by glacial movements. This rare ore deposit is world renown and thought to
be the largest and purest body of ore in New England. It is located on a 3.7 acre parcel in
Cumberland, Rhode Island 02864 near the intersection of West Wrentham Road and
Elder Ballou Meetinghouse Road It is about three miles east of Woonsocket, R.I., four
miles SW of the NE corner of R.I. and one mile from the Massachusetts state line. It is
the world’s only known site of Cumberlandite rocks. The area is aka “Iron Mine Hill. It
is classed as a variety of ferrogubbro and is an porphyritic igneous rock composed of
crystals white plagioclase feldspar in a finer-grained groundmass of magnetite, ilmenite,
and olivine that was “stewed in its own juices”. The feldspar and olivine changed to a
fine-grained serpentine. The rocks are black and gray-black color, heavy and slightly
magnetic. Attraction to a magnet can be used for means of positive identification.

Cumberlandite is commonly mistaken for a meteorite. This is because it has intense
magnetic susceptibility (property), its high specific gravity, and common pitted nature.
Even Wadsworth (1861) classed it as a “terrestrial pallasite” because Cumberlandite had
a texture similar to pallasite type of meteorite. Furthermore, Jackson thought that
Cumberlandite would grade in depth into an unoxidized metallic iron.

This site has been visited by many schools so students can learn about Cumberlandite and
glacier movements. Also of academic interest is the titanium content since it is one of the
industry’s most valuable metals.

It has been reported that these extremely rare rocks were deemed sacred by the Nipmuck
Indian Tribe. Cumberlandite was also used as early as 1703 for cannons, weapons and
farm tools during the Revolutionary War when it was recognized as a possible ore of iron.
It was mixed with hematite from the Hopkins Iron Mine in Cranston, Rhode Island and
was forged by Philip Brown at Abbott’s Run in Cumberland. Because it has alot of
titanium, which made it very costly and hard to smelt. Sadly a furnace explosion killed
Philip Brown in 1763. Cannons made of Cumberlandite were also used in the siege of
Louisberg in 1745. Sometime later, John Brown of Providence, R.I., was contracted for
iron used in cannons by the U.S. Government. He used a mixture of Cumberlandite and
Cranston ores and smeltered them in Easton Massachusetts. Most of the hill was reported
to be quarried for road metal by the Cumberland Iron Trap Rock Company.
Cumberlandite was used as gravel for the old Narragansett Race Track parking lot in
Pawtucket, R.I. The Iron Mine Hill outcrop, elliptical in cross section, was estimated to
be approximately 1,200 feet long on its major axis, and 500 to 600 feet on its minor axis.
Jackson (1840) calculated the mass of porphyrytic magnetic iron ore, 462 feet long, 132
feet wide and 104 feet high with 6,342,336 cubic feet of ore visible. It has a specific
gravity of 3.82-3.88 giving it tonnage of approximately 7,641,488 tons. Jackson’s
analysis stated this would yield about 3,000,000 tons of ore and over 1,000,000 tons of
titanium. I have identified over 50 grave headstones made of Cumberlandite and estimate them
to be over 225 years old.