Is lapis lazuli the same thing as lapis linguis?

Nope. Lapis Linguis is another name for Azurite. That is a blue mineral which was used for example as blue color pigment in the middle ages.

Lapis Lazuli is also a blue mineral, chemically similar to Azurite. But not exactly the same. And the color of Lapis Lazuli is ultramarine, not azure. Lapis Lazuli is rarer and more precious than Azurite.

Here’s one example of Lapis Lazuli: http://funadvice.com/r/157en9mago0

Azurite withers and becomes covered with green Malachite crystals while Lapis Lazuli doesn’t wither at all. Azurite turns dark, almost black if heated Lapis Lazuli remains blue in heat. Other than that, it is hard to tell one from the other.

So if you buy a brooch that has a “Lapis Linguis” stone in it, it should be noticeably cheaper than the same brooch with a “Lapis Lazuli” stone. Even though they may look extremely similar.

And, Oh… here’s a picture of Lapis Linguis (Azurite) with noticeable green stains: http://funadvice.com/r/157enfi459f

Azurite that is not withered looks like this: http://funadvice.com/r/157enfi46g3