Diabase is a hard, brittle rock used as a base component for
construction of roads and for building foundations.
The crushed-stone quarries that extract diabase are a substantial
economic resource. Loudoun County diabase is some of the best rock
for concrete and road base material found on the East Coast.
Continuing construction activities in the greater Washington area
will ensure that diabase continues to be an important local
economic resource.
Formed by hot magma [lava] 200 million years ago, diabase is
composed mainly of pyroxene, a dark mineral containing iron, and
plagioclase, a lighter mineral in weight and color. Other minerals
lending it its green-black color are epidote (green) and hornblende
(black). The composition varies naturally-typically contains quartz
(crystalline silica).
These diabase intrusions are mafic igneous rocks that intruded into
the crust during the opening of the Atlantic Ocean. As Pangea broke
apart during the Triassic and Jurassic, a huge system of sags
opened up in the crust. These low spots were the sites of (a)
intense sedimentation, since water flows downhill, and (b) mafic
igneous intrusions, since the thinned crust allowed decompression
melting of the underlying mantle. (Partial melting of an ultramafic
source usually yields a mafic distillate.)
The entire system of failed rift valleys extends along the same
trend as the Appalachians, but further east, all the way up to the
Bay of Fundy. Collectively, they are called the Newark Supergroup,
after one of the larger rift basins in Newark, New Jersey. Dirty
sandstones filling that basin were the source of all the 'brown
stone' that made the brownstones of New York City. Locally, in our
own Culpeper Basin, the main rock that is quarried is diabase,
which has a coarser crystal size than basalt, but smaller crystals
than a gabbro. It is distinguished by a lot of pyroxene. (1)
NaCa5Zr4Si16O40(OH)11·8H2O
Loudoun’s own species of rock! Loudounite
NaCalraSi,uOoo(OH),r.8HrO is a new species from the Goose Creek
quarry, Loudoun County, Virginia, where it occurs as green to
color-Iess spherules associated with actinolite. chlorite and
ancylite in diabase. (2)
The area now known as Loudoun County has had a long and complex
geologic history. The oldest rocks were folded and thrust up into
mountains over 1 billion years ago, eroded to flat plains, and
lifted up into mountains again. Other, younger rocks were made from
sediments deposited in ancient seas and then turned into rock under
heat and pressure. Later, molten rock from deep within the earth
forced its way up toward the surface through these older rocks
before slowly cooling. These geologic processes, some of which
continue today, shaped the land that we now live on.
The eastern half of Loudoun County is located in the Piedmont
physiographic province and the western half in the Blue Ridge
physiographic province. The Bull Run fault, coincident with the
eastern edge of the Catoctin Mountain, forms the boundary line
between the two provinces. Topography in Loudoun varies with
elevations ranging from 180 feet above sea level in the east (at
the Potomac River) to 1,900 feet above sea level in the west (along
the crest of the Blue Ridge). Major drainage systems include Broad
Run, Goose Creek, Catoctin Creek, and Bull Run. These drainage
systems and all of the smaller ones in Loudoun County are part of
the Potomac River Basin.
Bedrock geology and soil have a close relationship because all soil
material, except for the organic component, was derived from
rock.
The crushed-stone quarries that extract diabase are a substantial
economic resource. Loudoun County diabase is some of the best rock
for concrete and road base material found on the East Coast.
Continuing construction activities in the greater Washington area
will ensure that diabase continues to be an important local
economic resource.
This quarry was an important source of freight for the W&OD
Railroad, which closed in 1968. Diabase or Traprock an igneous
rock, is the primary product of the quarry.(1)
Please see the hints/spoiler information for details on where the
description information was pulled.
Questions:
1) Take a look at the two paths making up the W&OD Park (Bike
Path & Bridal Path). Which of the two paths are made from the
rock quarried from this site?
2) From the overlook, how many different layers have been dug by
the miners?
The following questions can be answered from the signage at the
listed waypoint.
3)What was the name of this quarry in the 1940's-1960's? Why was it
named this?
4)What kind of train took the gravel from the quarry?