Olive oil will harden at refrigerator temperatures -- around 37 degrees F. Water is a pure substance, so it freezes at an exact temperature. Olive oil is a complex mixture of oils and waxes. The heavier oils and waxes will form needle-like crystals as the temperature is lowered, then the other oils will start to settle out. Winterization is the commercial process whereby these waxes are removed to keep the oil clearer when stored on a cold shelf. It is used mostly for aesthetics and to improve mixing when combined into mayonnaise, sauces, and dressings.
Because olive oil is a natural product and different from year to year even from the same bottler, each batch of oil will "freeze" at a different temperature. There is no exact freezing temperature. Freezing olive oil will not harm it; it will actually prolong its nutritional benefits and its flavor. It is a myth that the freezing point of olive oil can be used to predict whether it is pure, virgin or extra virgin.