Quick answer: Pennsylvania is one of America’s most important mineral states. It led early U.S. iron production from furnaces fed by the Cornwall iron mines, supplied most of the world’s chromite in the early 1800s from the State Line serpentine district, and still holds nearly all U.S. anthracite coal. Its quartz comes from veins and pockets across the state.
Pennsylvania rarely comes up alongside Arkansas or Herkimer when people talk about quartz, but few states have a richer mineral history. For much of the eighteenth and nineteenth centuries it was one of the engines of American industry, and it was all built on what came out of the ground.
Want the full picture? See Quartz: The Complete Guide.
Iron: Cornwall and the early furnaces
The Cornwall iron mine in Lebanon County worked a large deposit of magnetite from the 1740s until 1973, one of the longest-running iron mines in North America. Iron from Cornwall and dozens of smaller mines fed charcoal furnaces across the colony, producing iron for tools, stoves, and cannon during the Revolutionary War. See magnetite for the mineral itself.
Chrome: the world’s early supplier
In the early 1800s, deposits of chromite in serpentine rock along the Pennsylvania-Maryland border became, for a time, a leading source of the world’s chromium, used then mostly for pigments. The serpentine belt around the state line produced unusual minerals too, and old chrome mines in southern Lancaster County are known to collectors for rare nickel and magnesium minerals.
Lead, zinc, and the Phoenixville mines
Near Phoenixville in Chester County, the Wheatley and neighboring lead mines of the nineteenth century produced some of the finest American specimens of pyromorphite, anglesite, and wulfenite. They are considered classic localities, and old specimens are prized. Our post on sulfide minerals explains the ores involved.
Coal: anthracite country
Northeastern Pennsylvania holds most of the anthracite coal in the United States, a hard, high-carbon coal formed as older coal beds were squeezed and heated during Appalachian mountain building. Anthracite fueled homes, railroads, and steel mills for generations. Coal-region shales also yield well-preserved fossil plants, often with delicate fern impressions.
Where Pennsylvania quartz comes from
Quartz is abundant across the state. Much of it formed in veins, where hot fluids moving through cracks during mountain building deposited silica, as described in hydrothermal veins. The Piedmont region in the southeast is especially rich in quartz veins, and clear, milky, and smoky crystals turn up in fields, road cuts, and old quarries. Pennsylvania quartz parcels usually show classic prismatic habit with the variations described in crystal habit, and sometimes the ghostly growth outlines explained in phantom quartz.
Collecting in Pennsylvania today
Many historic localities are now built over or closed, but collectors still find quartz, garnet, and other minerals in the state, often through club field trips that arrange access to quarries. As always, get permission first. For the wider region, see rockhounding the Northeast.
