The majority of roofing slate in the United States is quarried in the Northeast region.  In Canada, the Glendyne quarry is the largest producing slate quarry.  In this post we will recap recent visits to various quarries in places such as Pennsylvania, Vermont, and Quebec, Canada.


Pennsylvania Slate

slateroofbibleFirst, I began with the PA slate quarries of Penn Big Bed found in Slatington and Pen Argyl.  PA quarries were producing over half a million square back in the early 1900’s and there were over 100 beds being worked on.  This number has shrunk to 2 to my understanding.  Joe Jenkins book the Slate Roof Bible is also an excellent resource for information on slate from various areas.

The quarries are only about an hour and a half north of Philadelphia so it was not long of a drive. I arrived at Penn Big Bed and was shown around the facility and explained that the slate from this region is softer than most Vermont slate and easier to work with. PA slate can be used for blackboards, crafts, flooring tile, roofing material, turkey calls, as well as many other uses. This winter was horrific for the PA quarries and they were shut down from January until June. Below are some pictures of the quarry frozen over.

Ice Filled Slate Quarry

Ice filled slate quarry

Slate Quarry

100+ft of ice

This has left the producers in an unfavorable position because they were unable to supply customers throughout that period of time and now have a backlog of orders. Being unable to fill orders disrupts cash flow and production. Even though there is still demand for PA slate, it is difficult to quarry enough slate for supply. Quarrying slate in Pennsylvania has seen better days.


Vermont Slate

Taken at a slate quarry in Vermont that produces both black and green slate

Taken at a slate quarry in Vermont that produces both black and green slate

This picture is taken of a Vermont quarry that has been worked on for over 20 years.  It produces both black and green slate in different areas of the quarry.  A Vermont quarry can typically produce a couple hundred square of roofing slate a week.  This is minuscule compared to a Spanish quarry which can produce over a thousand square a day.  This wide margin is because roofing slate is much more prevalent in Europe and there are many more employees working a quarry.  The process used to mill it is also much more automated than here in the US which adds to production.

There are still many quarries found throughout “Slate Valley” which primary is found in the cities of Granville, NY, West Pawlet, VT, and then north to Fair Haven, VT. The area is very well known for slate because of the high quality of material as well as the variety of colors produced. Quarries in this area are once again confounded with the issue of production in that it’s difficult to keep up with it. For instance, if a big government building a needs a thousand square of roofing slate, this could take the quarry weeks to produce and orders are still coming in.




Glendyne Quarry – Quebec, Canada


Glendyne Quarry is the largest operating slate quarry in North America.  It is located in Saint-Marc-du-Lac-Long, Quebec, Canada.  Glendyne has an exclusive distribution agreement with North Country Slate for the North American market.  Internationally, Glendyne sells into a number of countries including, Belgium, Canada, France, Germany, Holland, Luxembourg etc.   Their slate is an S-1 grade (>75 yr durability) stone with a dark grey and hint of blue finish, free from pyrite and any other metallic intrusion.

Glendyne Quarry

Quarry producing roofing slate

Core Sample Shed

Glendyne routinely takes core samples to insure the highest qualities. This is a core sample shed with hundreds of cores

Finished Product on skid

A skid of 7mm thick slate to be exported to the UK

Final Inventory

A field of inventory skidded up and ready to ship


Glendyne is striving to continually reduce its waste in the quarry.  They currently operate at approximately 90% waste (many quarries operate at 95%) and they are projecting this number to decrease to 0% waste by year 2020.  This is done by finding alternative uses for the stone and by better methods of extracting.  This seems like quite a lofty goal, but Glendyne is working very hard to achieve a more sustainable, eco-friendly quarry.  Inside the mill, the selection process and cutting techniques are very similar to those used in the Spanish quarries.

Hand Splitting with a Slate Chisel

The hand splitting process is incredibly simple and leaves a very smooth surface thin slate

Walkway Stone

Not all slate is split for roofing. These blocks may be used and walkways/steps