1. mineralogy-the branch of geology that studies minerals: their structure and properties and the ways of distinguishing them. geology-a science that deals with the history of the earth as recorded in rocks.geode - (mineralogy) a hollow rock or nodule with the cavity usually lined with crystals.ineralogy-the branch of geology that studies minerals: their structure and properties and the ways of distinguishing them. geology-a science that deals with the history of the earth as recorded in rocks. geode - (mineralogy) a hollow rock or nodule with the cavity usually lined with crystals.