| PITCHBLENDE | Blackish mineral which is the principal source of uranium and radium (11) |
| PENTLANDITE | Brownish-yellow mineral which is the principal ore of nickel (11) |
| MANGANITE | Blackish mineral which is a source of manganese (9) |
| GALENA | Grey mineral which is the chief source of lead (6) |
| NERVE | (and 6 Across) R could be the principal source of control (5,6) |
| NERVECENTRE | Aggregation of neurons forming principal source of control of complex activity (5-6) |
| HEADSTREAMS | The principal sources from which larger flowers develop (11) |
| ALEXANDRITE | A dark green mineral which, along with pearl and moonstone, is the birthstone for June (11) |
| ATLANTIS | A legendary island in the Atlantic Ocean, lying west of the Strait of Gibraltar. The principal sources for the legend are two of Plato's dialogues, Timaeus and Critias. (9) |
| ACHILLES | He is the principal character in Homer's Iliad, son of Peleus, king of the Myrmidons in Thessaly and Thetis. He and his closest friend and lover, Patroclus, joined the Greeks in the Trojan War. Who is |
| TOULOUSE | Which is the principal city of the Midi-Pyrenees region of France? (8) |
| TIANANMEN | The Gate of Heavenly Peace which is the principal entrance to Beijing's Forbidden City |
| KRILL | Shrimp-like marine crustacean which is the principal food of whalebone whales (5) |
| EBRO | Which is the principal river of north-east Spain? (4) |
| ANDES | Which is the principal mountain chain of South America? (5) |
| ILMENITE | Which is the principal ore of titanium, also called iron titanate (8) |
| REALGAR | Rare orange-red mineral which is an important ore of arsenic (7) |
| FELDSPAR | Mineral which is a constituent of granite (8) |
| COPPER | What metal was named after Cyprus, the principal source in Roman times? (6) |
| DAIL | The ___ Eireann is the principal chamber of the Irish parliament, the Oireachtas |
