Skil Craft Geology Lab Set Circa Late 1960s/Early 1970s

Judging by the fashion it looks like circa 1970. And once again Skil Craft featured a boy and a girl as opposed to just boys as their competitor Gilbert did. This of course is a Geology set. It came with a fine set of various rocks/minerals along with a special scale and some this and that. The scale, seen in photo #3, is called a Jolly Scale and is used to to measure specific gravity. Not quite sure what that is, probably has something to density..
One note about this set is that is difficult to open as the contents all fall out as the specific gravity works against them.