Thomsonite

Thomsonite is a rare semiprecious gemstone in the zeolite family. It is a sodium calcium aluminosilicate with a vitreous (glassy) to pearly luster and an orthorhombic crystal form which usually grows as long thin bladed crystals forming radial aggregates. It may be opaque to translucent or transparent, has a hardness of 5 to 5.5 and takes an excellent polish.

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​In the mid 1990's, I had the good fortune to live for 4 years in Nova Scotia, close to the ocean. Most of my free time was spent rockhounding on local beaches, collecting amethyst, agate and zeolite minerals. It was in my last summer there that I learned about thomsonite, and by the time I left Nova Scotia I brought with me about 25 pounds of these fascinating pebbles. Over the past few years I have finally had the time and facilities to start polishing, and the results have exceeded my expectations. I now have over 200 hand polished stones and over 1,500 good sized (1/4” to 1“) quality tumbled stones. Additionally, some beautiful pebbles picked directly off the beach, with a soft silky luster, have already been naturally polished to the point where they require no further work. Shimmerocks is excited this year to introduce this amazing stone onto the market.

 

Although thomsonite is found in many places around the world, gem quality material occurs in only a few locations. This is what makes the stone so rare and valuable.

 

Gem grade thomsonite occurs along the north shore of Lake Superior in a few places – on the Keweenaw Peninsula and Isle Royale in Michigan, and along a small stretch of beach near Grand Marais in Minnesota. This material has long been used in making jewellery. It occurs as nodules in basalt, usually small in size, and typically showing a pattern of concentric “eyes” in a wide range of colours including white, pink, green, pale yellow, light grey, pale orange and even black and sometimes blue. While some loose nodules may be found, most must be extracted from the basalt matrix. The stones are highly prized by collectors, and are typically valued at $5 to $20 per gram. Tumbled stones with desirable colours and patterns can sell for hundreds of dollars.

 

Cabochons of natrolite, another related zeolite, from a 2020 discovery in Indonesia, were originally thought to be thomsonite. This material is generally uniform in colour and pattern and is sometimes referred to as “pink larimar” which it resembles. Although sometimes still sold as “thomsonite”, it has now been identified as a unique variety of pink natrolite.

 

Thomsonite from Nova Scotia is much less well known and has not been commercially marketed, but has proven to produce beautiful stones. It occurs as nodules in basalt which is exposed around the Bay of Fundy. As erosion by the ocean wears away the basalt cliffs, and the rocks are further tumbled about in the waves, the basalt is worn away leaving nodules of thomsonite fully or partially exposed. These can be collected from gravel beaches along the Bay of Fundy shore. The nodules may be tumbled or hand polished to produce finished stones, some as large as 1.5 inches, suitable for jewellery. Usually the shape of the nodule will determine the shape of the finished stone. Nova Scotia thomsonite is typically white or pink but colours can also include grey, tan, brown, red, orange, yellow, gold, and clear. The stones display a wide variety of patterns. Some have “eyes” which may appear to move as the stone is turned. Many show chatoyance (cat's eye effect) or a pearly luster. Other stones may have a bladed structure, or colour banding, or a mottled colour pattern. Every stone is unique.

 

Nova Scotia thomsonite differs from Minnesota in size (they are usually larger), in colour (they do not include green, blue or black), in shape (the nodules tend to be more more irregular in shape), and in pattern (they show much greater variety).