Olive oil congeals in refrigerator?

Yesterday,I made a vinaigrette dressing with Balsamic vinegar, olive oil, garlic, salt and pepper. I put in the refrigerator after I was finished and I just took it out this afternoon. It appears that the olive oil has congealed and is no longer liquid. After whisking it with a fork it returned to it's more familiar density. Is it still okay to eat, it may seem like a silly question, but I just want to be sure that its a normal phenomenon. Thanks for your answers.