The following write up on the Mineral Record website (www.minrec.org)  "Whats New in the Mineral World" by Thomas Moore:

 Time now, courtesy of Lehigh Minerals, to familiarize ourselves with the products of a long-gone Pennsylvania locality. Or, in the case of old Pennsylvanians like the present writer, to re-familiarize ourselves with a place which we may not have known well enough, or have visited often enough, in the 1960's, when it last produced its distinctive, often superb specimens. I refer to the Keystone quarry near the village of Cornog, Chester County, where road-metal rock was taken from a banded hornblende gneiss with interlayered amphibolite and lenses of blue quartz. Commercially active from 1908 to 1968, the Keystone quarry had Alpine-type clefts from which came excellent (though invariably iron oxide-stained) specimens of adularian orthoclase, byssolitic actinolite, clinozoisite and prehnite. Very rarely, too, its clefts gave up world-class crystal clusters of colorless and transparent fluorapatite that, with their inclusions of acicular actinolite, very closely resemble the fluorapatites of the famous Knappenwand, Untersulzbachtal, Austria epidote occurrence. Lehigh Minerals recently purchased a hoard of about 500 "Cornog" specimens from an old Pennsylvania collection; previewed at last year's Denver show, the hoard, or anyway the best of it, was posted on the website (www.lehighminerals.net) just after the Tucson Show. Opaque milky white adularian orthoclase was found at Cornog as curious-looking reticulated groups of spindle-shaped crystals, these little clusters available with Lehigh as self-contained thumbnails or as thick piles on matrix plates to 7 cm across. Inevitably, the fibrous "byssolite" variety of actinolite accompanies the orthoclase, as cobwebby aggregates around the bases of crystals and/or as individual, delicate, upstanding needles. Clinozoisite comes as dense, parallel groups of very thin, lustrous, gray-green prisms surrounded by byssolitic actinolite or, in a few specimens, as individual, thicker prisms to 5.5 cm long. Spiky little crystals of yellow-green prehnite to a few millimeters, and tiny goethite pseudomorphs after pyrite, sometimes are seen also suspended in the actinolite clouds…but it grieves me to say that this specimen lot includes no fluorapatite specimens (at least that we are to know of). This is a suite which deserves checking-out, at the least for elementary educational reasons, if not also because it may be your first and last chance to score something from this significant, never well enough known, locality.