05/10/2026
Feldspar is not just one mineral, but a large group of minerals (2). In fact, more than half of the Earth’s crust is made of feldspar (1)!
The term feldspar is used to describe any mineral made of aluminum, oxygen, and silicon (2) that contains calcium, sodium, or potassium (1). There are two main types of feldspar: plagioclase feldspar (ie, oligoclase, labradorite, etc.) and alkali feldspars (ie, orthoclase, microcline, etc.) (2). Amazonite (pictured) is a variety of microcline, an alkali feldspar (4).
Feldspar can be used to make glassware, pottery, fillers, buildings, monuments, and even semi-precious gemstones (2).
The MacDonald Mine, located in Monteagle Township, was a feldspar mine from 1919 to 1928 (3). It produced approximately 5,000 tons of feldspar per year, as well as a diverse range of rare-element minerals (3).
You can check out many different specimens of feldspar at the Bancroft Gem & Mineral Museum, or go find some for yourself at the CN Rock Dump, just a few minutes' walk from the museum!
Sources:
(1) Dietrich, R. (2025, April 3). Feldspar. Encyclopedia Britannica. https://www.britannica.com/science/feldspar.
(2) Feick, K. (n.d.). Feldspar. University of Waterloo: Earth Sciences Museum. http://uwaterloo.ca/earth-sciences-museum/resources/detailed-rocks-and-minerals-articles/feldspar.
(3) Mindat. (n.d.). MacDonald Mine, Monteagle Township, Hastings Highlands Municipality, Hastings County, Ontario, Canada. https://www.mindat.org/loc-544.html.
(4) The National Museum of Natural History. (n.d.). Amazonite. Smithsonian Museum. https://naturalhistory.si.edu/explore/collections/geogallery/10002689.