One of the best-known Canadian gemstone localities is the Jeffrey (Asbestos) Mine in Val-des-Sources, Quebec. Although, asbestos production began in 1881, mineral collectors have only known about the presence of garnet crystals since about 1950. Grossular garnet in a variety of colours (orange, green, pink, colourless) and other fine crystals, such as vesuvianite and diopside, have been collected at the Jeffrey Mine over the decades since then.
Demantoid crystals were discovered much more recently (within the last couple of years) at the Jeffrey Mine. Demantoid is the green variety of andradite garnet. The demantoid gems offered for sale here were cut from this new find. Unlike the grossular garnet and vesuvianite, which occurs as complex, sharp, lustrous crystals within open cavities in the rock, the demantoid crystals have a frosted surface and occur as slightly rounded crystals encased in serpentine. Some even have fibrous, "horsetail-like" inclusions similar to those often seen the demantoid from Russia. Like the crystals, demantoid gemstones are generally small; most gems weigh less than a half carat. Only a couple of gems that weigh over 1 carat have been cut.
More information about these gems can be found in an article I wrote for "InColor" magazine, in January 2020, about Canadian gemstones. You can find the article here; "Colored Gemstones from Canada; An Update"