The blue one is interesting Richard. Chromium can be responsible for quite a few different colours in minerals including yellow ("chrome" cerussite), orange/red (crocoite), red (ruby), green (emerald, uvarovite, chromium grossular, diopside and others), green/red colour change (chrysoberyl var alexandrite), purple (stichtite), as well as the pale blue here. Some gibbsite, associated with crocoite, at Dundas, Tasmania, is a similar blue, so probably also due to chromium.
The blue one is interesting Richard. Chromium can be responsible for quite a few different colours in minerals including yellow ("chrome" cerussite), orange/red (crocoite), red (ruby), green (emerald, uvarovite, chromium grossular, diopside and others), green/red colour change (chrysoberyl var alexandrite), purple (stichtite), as well as the pale blue here. Some gibbsite, associated with crocoite, at Dundas, Tasmania, is a similar blue, so probably also due to chromium.
Thanks for that!
Another fascinating column, Richard! Always looking forward to your multifaceted comments!