Carna lies wedged across the mouth of Loch Teacuis in the middle of Loch Sunart, forming two narrow kyles which provide some of the trickiest rock-dodging for yachtsmen anywhere on the west coast. Moine schist bedrock of quartz-feldspar constitution, with mixed schists and mica schists in a west coastal strip. A north-south ridge divides the island in two. From the heather covered rocky peak of Cruachan Chàrna, there are extensive views over Oronsay, Loch Sunart, Morvern, Coll and Isle of Mull.