how to differentiate quartz and feldspar?
They change colour due to impurities only. Its odd for it to suddenly change colour without something to help it. If you left it by a strong heat source, say a cooker or hot radiator, that was ~60+ Celsius that could have caused a change in crystal structure. Or if you left it by a heat source while using bleach or something similar. My knowledge is limited but I hope this helps.
Could it be related to what you are wearing on a particular day? It may look pink if you happen to be wearing something red or pink. As far as I know, heat won't change the color of quartz like can happen with some other minerals (even then the temps involved are pretty high I believe, and probably not commonly encountered by jewelry in a house). Have you taken it off and held it in front of a white or neutral background to examine its color?
