There is an excellent post at Better Bibles Blog on translating Greek genitives. This may not sound the most exciting subject under the sun – but it is one of them. A genitive is a possessive structure such as ‘coals of fire’ (to quote the AV) and Greek uses them all over the place in situations where English would do something very different. Go on, have a read!
Link to Better Bibles Blog: Translating the genitive construction