Conway granite is a typically pink (or mesoperthitic)

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron- endmember annite, and the magnesium-endmember phlogopite; more al ...

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

."Conway Granite." Mineral Resources On-Line Spatial Data. U.S. Geological Survey. U.S. Department of the Interior. No date.
Accessed 2011-03-30. It is

amphibole Amphibole ( ) is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...

-free and of coarse

particle size Particle size is a notion introduced for comparing dimensions of solid particles ('' flecks''), liquid particles ('' droplets''), or gaseous particles ('' bubbles''). The notion of particle size applies to particles in colloids, in ecology, in ...

(with portions of the rock fine-grained or

porphyritic Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning ...

). Conway granite has a relatively high concentration of

thorium Thorium is a chemical element; it has symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive grey when it is exposed to air, forming thorium dioxide; it is moderately soft, malleable, and ha ...

, at about 56 (±6) ppm; this amount is not enough to make the granite dangerously radioactive, but it is sufficient to make the rock a low-grade (almost certainly not economic, at least in the early years) source of thorium for a

thorium fuel cycle The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural ...

. Geologist

Edward Hitchcock Edward Hitchcock (May 24, 1793 – February 27, 1864) was an American geologist and the third President of Amherst College (1845–1854). Life Born to poor parents, he attended newly founded Deerfield Academy, where he was later principal, ...

named the granite in 1877 after the town of

Conway, New Hampshire Conway is a New England town, town in Carroll County, New Hampshire, Carroll County, New Hampshire, United States. It is the most populous community in the county, with a population of 9,822 at the 2020 United States census, 2020 census, down from ...

, which is near where it is mined. The Old Man of the Mountain, a famous geologic feature in

New Hampshire New Hampshire ( ) is a U.S. state, state in the New England region of the Northeastern United States. It borders Massachusetts to the south, Vermont to the west, Maine and the Gulf of Maine to the east, and the Canadian province of Quebec t ...

, was made of Conway granite. (The rock formation collapsed in 2003.) Conway granite is found throughout the lower areas of the central White Mountains, such as Franconia Notch,

Crawford Notch Crawford Notch is a major pass through the White Mountains of New Hampshire, located in Hart's Location. Roughly half of that town is contained in Crawford Notch State Park. The high point of the notch, at approximately above sea level, is a ...

, the center of the Pemigewasset Wilderness, and the Saco River valley. Other exposures of the formation include the Belknap Mountains south of Lake Winnipesaukee.

References

Granite Igneous petrology of New Hampshire {{Petrology-stub