Cumberlandite
Cumberlandite is a type of plutonic rock known as a melanocratic troctolite, or melatroctolite, and is the state rock of the U.S. state of Rhode Island.[1][2] It is found in a 4-acre (0.016 km2) lot in Blackstone Valley, Cumberland, and traces scattered throughout the Narragansett Bay watershed. Due to its high amounts of iron, it is slightly ferrimagnetic.
Background
Cumberlandite is considered sacred to the Nipmuc tribe. [3][citation needed] Notably, during the 18th and 19th centuries, colonial settlers recognized its value as ore. Historical records reveal that as early as 1703, it was smelted and was later employed in the forging of cannons during significant events such as the Siege of Louisbourg in 1745 and quite possibly the Revolutionary War.[4]
Cumberlandite weathers to a brownish black with white crystals and has secondary chlorite and saussurite.[5] It is predominantly found in glacial deposits stretching from South of its origin to the Southern shores of Narragansett. Unlike other rocks in Rhode Island's glacial deposits, Cumberlandite is denser than common granites or metamorphic rocks. Its unique origin, distinct appearance, and ease of identification contributed to its selection as the Rhode Island state rock.
Petrology
Cumberlandite is an uncommon mafic igneous rock known as a melanocratic titaniferous magnetite troctolite, or titaniferous magnetite melatroctolite.[6] Troctolites are olivine-rich pyroxene-poor gabbros and are unusual rocks common in layered mafic intrusions believed to have formed as cumulates in a magma chamber. Cumberlandite has light phenocrysts of labradorite in a dark medium-grained matrix of magnetite, ilmenite, olivine, and hercynite spinel. Magnetite and ilmenite cumulates are also common in layered intrusions and these minerals can account for up to 70 percent of the rock's volume contributing to the rock's high density and magnetism. Locally the preferred orientation of the plagioclase crystals gives the rock a lamination.[7] The rock is part of the Esmond-Dedham Subterrane with an uncertain age from Late Proterozoic to Devonian and likely mid-paleozoic.[8][9]
References
- ^ Fun Facts and Figures about Rhode Island
- ^ Dietrich, R. (1986). "Rhode Island's State Rock and Mineral: Cumberlandite & "Bowenite"". Rocks & Minerals. 61 (5): 251–256. doi:10.1080/00357529.1986.11762723.
- ^ Ferguson, Joseph L. eReferenceDesk. https://www.ereferencedesk.com/resources/state-symbols/rhode-island/rock.html
- ^ Dietrich, R. (1986). "Rhode Island's State Rock and Mineral: Cumberlandite & "Bowenite"". Rocks & Minerals. 61 (5): 251–256. doi:10.1080/00357529.1986.11762723.
- ^ Dietrich, R. (1986). "Rhode Island's State Rock and Mineral: Cumberlandite & "Bowenite"". Rocks & Minerals. 61 (5): 251–256. doi:10.1080/00357529.1986.11762723.
- ^ R. V. Dietrich (1986) Rhode Island's State Rock and Mineral: Cumberlandite & “Bowenite”, Rocks & Minerals, 61:5, 251-256, DOI: 10.1080/00357529.1986.11762723
- ^ Dietrich, R. (1986). "Rhode Island's State Rock and Mineral: Cumberlandite & "Bowenite"". Rocks & Minerals. 61 (5): 251–256. doi:10.1080/00357529.1986.11762723.
- ^ Mineral Resources Spatial Data and Geology: Rhode Island; United states Geological Survey
- ^ Dietrich, R. (1986). "Rhode Island's State Rock and Mineral: Cumberlandite & "Bowenite"". Rocks & Minerals. 61 (5): 251–256. doi:10.1080/00357529.1986.11762723.