114 SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
more micaceous and the more quartzose beds are crystals, lenses, and particles of 
pyrite, numbering about 25 to each square millimeter and measuring up to 0.09 mm., 
rarely 0.15 and 0.42, with their longer axes parallel to the cleavage. These probably 
include a little magnetite. There are also biotite scales transverse to the cleavage, 
about 22 per square millimeter, and measuring up to 0.12, rarely 0.2 mm. Almost, if 
not quite, as abundant are plates and rhombs of carbonate. There are occasional 
scales of chlorite interleaved with muscovite, afewgrainsof plagioclase feldspar0.047 
mm., rarely one of zircon, some tourmaline prisms 0.014 mm. long, much extremely 
fine graphitic (or carbonaceous?) material, a few particles of hematite, and some! 
rutile needles. Sections parallel to the cleavage are unusually brilliant in polarized 
light, owing to the abundance of quartz, biotite, and carbonate. 
The chief constituents of this slate, arranged in descending order of abundance,; 
appear to be muscovite and sericite, quartz, biotite, carbonate, graphite (or carbons! 
ceous matter)-, pyrite, chlorite, magnetite, with accessory plagioclase, zircon, hema-j 
tite, tourmaline, and rutile. 
The Fontaine quarry of A. L. Pitts has a length of 300 feet along the cleavage, a 
width of 200, and a depth of about 100. Bedding and cleavage strike N. 34° E., dip 
80° SK. The quart/ veins also contain calcite. 
The slate from this quarry is very dark gray with a greenish hue, and to the' 
unaided eye has a granular sparkling crystalline texture and a roughish, but very] 
lustrous, cleavage surface. It is slightly graphitic (or carbonaceous). The sawn 
edge shows pyrite. It contains rare particles of magnetite, does not effervesce ill 
cold dilute hydrochloric acid, and is very sonorous. 
Under the microscope the Fontaine quarry slate shows alternating bedlets of tine, 
more muscovitic, and coarser, more quartzose, material, the former having a brilliant] 
aggregate polarization. Much of the mica is in the form of muscovite rather than: 
sericite, particularly in the quartzose beds. These beds are parallel to the cleavage. 
Quartz fragments abundant, measuring up to 0.09 and 0.12 mm.' Most conspicuous 
scales of biotite lie across the cleavage, usually up to 0.2 by 0.09 mm. and averaging 
about 10 per square millimeter. Lenses and crystals of pyrite, often surrounded n 
secondary quartz, about tin per square millimeter and measuring up to 0.076 by 0.03 
rarely 0.34 by 0.03 mm., with their longer axes in the cleavage. A few scales of 
chlorite, interleaved with muscovite, lying across the cleavage and up to 0.3 mm. 
Some carbonate in the coarser bedlets, occasionally with inclusions of an opaquel 
mineral (graphite, pyrite, or magnetite ). Much graphitic (or carbonaceous) matter) 
i i very minute particles. Some hematite and a few crystals of tourmaline, 0.02 by 
0.006 mm. 
The chief constituents of this slate, arranged in descending order of abundance, 
appear to be muscovite and sericite, quartz, biotite, carbonate, pyrite, graphite (or 
carbonaceous matter), chlorite, magnetite, hematite, with accessory tourmaline. 
A specimen from an exceptional bed in the same quarry shows a wrinkled surface i 
from the abundance of biotite lenses measuring a half inch in length by a twentieth! 
in width at the center. George II. Williams found the joint faces at the old Rob-' 
erts quarry covered with pyrite and crystals 1 mm. long, which when analyzed proved'' 
to be Ti0 2 and which he determined optically as anatase. 
Although the Arvonia slates, as shown by the above determinations, contain some* 
carbonate, that does not include any appreciable amount of ferrous carbonate, fo?< 
some of these slates put on the old Richmond theater over sixty years ago, when i 
removed within the last three years, did not show any discoloration whatever, and' 
some have been on buildings near the quarries over a century without losing any 
of their blackness. Their highly crystalline character also implies strength and' 
durability. 
a Anatase from the Arvon slate quarries, Buckingham County, Va.: Am. Jour. Sci., 3d ser., vol. 42, »: 
1891, p. 431. 
