Guilford Quartz Monzonite

Guilford Quartz Monzonite
Stratigraphic range: Silurian
Photographed on a boulder at the old Guilford Quarry on Guilford Road, Columbia, Maryland.
Typeigneous
Lithology
Primarymonzonite
Location
RegionPiedmont of Maryland
Extentcentral Maryland
Type section
Named byCloos and Broedel, 1940[1]
Outcrop of Guilford Quartz Monzonite in Kings Contrivance Village, Columbia, Maryland
Historical photo c. 1910 of the Guilford Quarry while in operation
Polished slab from the Guilford Quarry (1898). Width is approximately 10.7 cm.
The old Guilford Quarry in January 2013, facing north.

The Guilford Quartz Monzonite is a Silurian or Ordovician quartz monzonite pluton in Howard County, Maryland. It is described as a biotite-muscovite-quartz monzonite which occurs as discontinuous lenticular bodies[2] which intrude mainly through the Wissahickon Formation (gneiss).

The extent of this intrusion was originally mapped in 1940[1] as the "Guilford granite". It was given its current name in 1964 by C. A. Hopson.[3] Hopson grouped the Guilford Quartz Monzonite with the Ellicott City Granodiorite and the Woodstock Quartz Monzonite as "Late-kinematic intrusive masses."

  1. ^ a b Cloos, Ernst, and Broedel, C.H., 1940, Geologic map of Howard County and adjacent parts of Montgomery and Baltimore Counties (Maryland): Maryland Geological Survey County Geologic Map, 1 sheet, scale 1:62,500
  2. ^ USGS Mineral Resources On-Line Spatial Data
  3. ^ Hopson, C. A., 1964, The crystalline rocks of Howard and Montgomery Counties: Maryland Geological Survey County Report, 337 p., (Reprinted from Cloos, Ernst, and others, "Geology of Howard and Montgomery Counties," p. 27-215)