Larimar is a blue variety of the silicate mineral pectolite. It's coloring can range from dark blue, to blue-green, and sky blue. With a hardness of 4.5-5, it's a popular jewelry stone. The blue coloration seen in pectolite from the Dominican Republic (Larimar) is due to traces of copper substituting calcium. The highest quality are dark blue and translucent, but sky blue coloration with cloud-like patterning is also very valuable. The higher the contrast, and more intense the blue - the higher (and rarer) the quality. Though pectolite is found in many locations, Larimar (this blue pectolite variety) can only be found in the Dominican Republic, in the Caribbean, and is locally abundant.1
Inclusions: There are often red dendrites (hematite) that create fern-like plume patterns around the edges of the blue pectolite. This is because there is abundant hematite in the basalt deposits just above the pectolite-bearing veins. Sometimes there are also white to grey patches of calcite, light gray natrolite, or microscopic black flakes of chalcocite.2
FYI: The blue color is photosensitive and will fade with time if exposed to too much light/heat!
Image: (Left) high quality Larimar with bright blue and high contrast; (right) low grade Larimar with dull blues, more matrix and white/grey.
I'm not aware of any Larimar synthetics, and I honestly don't personally encounter a lot of fake Larimar specimens - it seems to mostly occur with glass and ceramic simulants. Larimar has such a distinctive appearance, that it's quite easily distinguished from any similar simulants.
As of an article in "Gems & Gemology" by Woodruff and Fritsch (1989), there weren't any known efforts to commercially enhance blue pectolite. Exposure to flame and irradiation doesn't enhance the color, and there was no evidence of dyeing low-quality material with a copper sulphate.
Pictured below are a couple examples of simulated Larimar found on eBay, but both were marked as "simulated Larimar".
Image: (Left) simulated Larimar pendant on eBay, (right) simulated Larimar earrings on eBay.
Woodruff and Fritsch (1989) noted that there were a couple of man-made glasses that could perhaps be mistaken for Larimar: "Victoria stone" and "Imori stone". But this example pictured below (left) was clearly labelled on Etsy as "Victoria Stone", with no attempt at selling it as Larimar. As you can see, it still looks quite different from the real deal. Beside the "Victoria stone" (on the right) is a photo of "Imori stone" found from eBay, and it also was clearly labelled as "Imori stone", with no attempt at passing it off as Larimar.
Image: (Left) Victoria Stone pendant from Etsy (SilverCoveLtd); (right) Imori stone piece from eBay
Both "Victoria stone" and "Imori stone" differ quite a bit in appearance from true blue pectolite (Larimar), so even if folks try to pass them off, they're quite easy to distinguish. Though I haven't seen any evidence of folks using these as Larimar firsthand, as these man-made glass materials seem quite expensive.
From what I've seen at gem shows (sorry I don't have any photos), there will occasionally be super cheap beaded jewelry with blue plastic that is meant to somewhat resemble Larimar, but it's usually quite easy to spot and you can always use the touch test: Larimar is a stone and is cool to the touch, where plastic is room temperature.
That was a short blog in comparison to some of the deep dives about Moldavite, Malachite, etc. but Larimar isn't a highly faked stone from my experience. Price is always a red flag as well - Larimar isn't cheap, especially for high-quality pieces, but lower grade can be quite affordable.
Spiritually, Larimar is the embodiment of Caribbean Sea tranquility. It is said to facilitate clear communication and support a state of confident well-being.
Do you have any additional questions about Larimar you'd like me to cover? Please comment below and I'm happy to answer any questions and/or add to this post with more specifics.
1 Source: gemsociety.org [https://www.gemsociety.org/article/pectolite-jewelry-and-gemstone-information/]
2 Source: Woodruff & Fritsch; gia.edu [https://www.gia.edu/gems-gemology/winter-1989-blue-pectolite-woodruff]