I think Hydrofluoric acid is probably the substance you're describing which leaches the calcium out of your bones. It will certainly burn you too though. It's a common byproduct from heating fluorinated gases and is sometimes used in its own right for wet etching.

As an aside, I love it when they tell you in the safety WBT what the highly toxic gas smells like.

For lower concentrations (< 50%) HF burns aren't always immediately visible (and often not immediately painful), which can delay treatment as people may assume it's not serious.