Amethyst & Rose Quartz Thumb Palm Stones

These are two palm thumb , stones, both naturally carved oval shaped. Amethyst thumb stone . Rose quartz thumb stone. The amethyst stone is about 4.5cm / 1.77in,chest. The rose quartz is about 3.5cm / 1.37in. They are about 0.7-0.8mm / 0.27-0.31in thick and weigh about 15-20g. Both in matte finish. I have a set myself and display it it my fish tank. The fish always swim around it and are curious and baffled by these stones? Some of my gold fish want to eat them? For gifts, meditation, yoga, mantel display, aquariums , personal use?