Genuine amber contains circular cracks in it which are caused by the heating process. Sometimes you see small black cracks which're filled with tiny crytals. Insect bodies are sometimes trapped in real amber as well. These get covered with a white coating, which is normal, and caused by decay. Two easy tests for you - scratch your piece of amber with a pin. If it doesn't scratch - it's fake (such as glass). The second one, is to heap about 7 teaspoons of table salt into half a pint of water. Stir it round, then drop the amber into it. If it's real, the amber'll float.