The amphiboles are a group of chain silicate minerals with some substitution of F and Cl for OH. They have a general formula of (W,X,Y)7-8(Z4O10)2(OH)2 where W represents large cations like Ca and Na, X represents smaller cations like Mg and Fe2+, Y represents Fe3+, Ti, and Al, and Z represents Si and Al. Amphiboles are distinguished from pyroxenes by having a different Si:O ratio and containing essential OH groups in their structure. Common amphiboles include hornblende, tremolite, actinolite, anthophyllite, cummingtonite, grunerite,