the best person in the world. he's one in a million. he's polite, kind, thoughtful, and freaking hilarious. there is never going to be anyone like him. i love him more than any boy.
Slate is a rock, so you won't find it listed on the Mohs Scale, because that scale of hardness applies to minerals. I'll go out on a limb though, and suggest that slate is probably around 2 to 3 or so, but this will be variable, depending on the quality of the slate, and degree of weathering, etc. Slate is a rock, so you won't find it listed on the Mohs Scale, because that scale of hardness applies to minerals.
Permanent hardness is hardness (mineral content) that cannot be removed by boiling. When this is the case, it is usually caused by the presence of calcium sulphate/calcium chloride and/or magnesium sulphate/magnesium chloride in the water, which do not precipitate out as the temperature increases.