User blog comment:Wildoneshelper/Guess the Object (Round 2)!!/@comment-4189499-20140614072425/@comment-4189499-20140615101247

Huuh, so bone's calcium phosphate. Ah well, I said that I wasn't sure on that one, since biology is one of the few areas of science I have little interest in, but whatever.

Also, it is not true to say that "only the Group I metals, ammonium and uranyl carbonates are soluble in water." First of all, most if not all of the halogens can be present in water in the ionic form, and so too can many metal ions such as calcium, silver and lead (first three that came to mind). How do I know this? Just under a month ago I had to memorise the tests to identify their presence in a water sample. If calcium is in the water, it can be identified by precipitating it with silver ions. The same goes the opposite way for silver ion. Lead can be identified by adding potassium iodide (KI) and seeing if it forms a yellow precipitate, and barium can be identified in a water sample by adding sulphate ions. Also, the presence of copper and iron ions in a sample of water can be easily seen by looking at the colour of the water: blue for copper, brown for iron. While it's true that these ions aren't soluble in all quantities or in the presence of all ions, unlike Group I metals, they do still dissolve to some amount. While calcium carbonate is insoluble in large quantities, and by large I mean more than a few ppm, it does still dissolve to a certain extent, and as I said before is responsible for water "hardness".