Leonard James Spencer, 1911 Encyclopædia Britannica, Volume 21… (1911)
“ A curious property is to be observed when a crystal of pharmacosiderite is placed in a solution of ammonia—in a few minutes the green colour changes throughout the whole crystal to red, on placing the red crystal in dilute hydrochloric acid the green colour is restored. Natural crystals are sometimes honey-yellow to brown in colour, but this appears to be due to alteration. ”
