The double chain silicates are formed so that many ionic substitutions are possible, therefore the chemical varieties are endless. All double chain silicates are in the amphibole group. These contain water and are formed at lower temperatures than olivines and pyroxenes. There are over thirty varieties. Some of the more well known are actinolite, of which nephrite jade is largely composed, and hornblende, found in basaltic lavas in mountainous areas of the world. Some very large rocks are mostly hornblende.
A bit warmer today. I may get back to the photographing of materials from Ely or whatever I can find.