Dedham Granite is a light grayish-pink to greenish-gray, equigranular to slightly porphyritic, variably altered, granite south and west of Boston, named for the town of

Dedham, Massachusetts Dedham ( ) is a town in and the county seat of Norfolk County, Massachusetts, United States. The population was 25,364 at the 2020 census. It is located on Boston's southwest border. On the northwest it is bordered by Needham, on the southwest b ...

Qualities

Dedham Granite includes dioritic rock near Scituate and Cohasset and Barefoot Hills Quartz Monzonite. Intrudes Zdi, Zgb, Zb, Zv. Extensive calc-alkaline plutons separated by Boston basin have long been mapped as Dedham. Those to the north of Boston and studied by the

US Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, an ...

, are referred to as Dedham North. Crystallization ages for the Dedham North suite (based on titanites and zircons) have been determined at 607+/-4 Ma, while ages for the Lynn are slightly younger at 596+/-3 Ma. Both are clearly part of the Late Proterozoic magmatic event. Dates on two samples from Sheffield Heights indicate that the diorite and granite are part of the Dedham North suite. The Dedham south and west of Boston has been dated at 630+/15 Ma. Dedham North Granite has a compositionally highly variable suite ranging from leucogranites to granodiorites, tonalites, and quartz diorite. The granites originated by partial melting of a sedimentary protolith, while the intermediate members show a mixing of granitic magma and mafic magma.

Uses

The rock has been used for many notable building projects in and around Dedham. It was used for St. Mary's Church (1880), St. Paul's Church (1858),

Memorial Hall A memorial hall is a hall built to commemorate an individual or group; most commonly those who have died in war. Most are intended for public use and are sometimes described as ''utilitarian memorials''. History of the Memorial Hall In the aft ...

(1868), the Boston and Providence Railroad station (1882), the Dedham Public Library (1888), and Trinity Church in Copley Square. There are several pieces of it arranged decoratively along East Street in Dedham, between High and Avery Streets. These pieces were remnants of the railroad abutment that was dismantled in 2008.

Plymouth Rock Plymouth Rock is the traditional site of disembarkation of William Bradford and the ''Mayflower'' Pilgrims who founded Plymouth Colony in December 1620. The Pilgrims did not refer to Plymouth Rock in any of their writings; the first known writt ...

is also a piece of Dedham Granite, having been moved to the coast by a glacier 20,000 years ago.

References

{{Dedham Geologic formations of Massachusetts Ediacaran geology Dedham, Massachusetts