Using the mortar and pestle, crush the coriander and fennel seeds together. Add the garlic cloves and crush until a paste starts to form.
Strip the leaves from the rosemary sprig and pick the leaves from the parsley and add to the mixture. Crush until they become incorporated into the paste. Add vinegar and olive oil and stir.
Put the olives in a small container and pour the marinade over the top. Refrigerate for at least 1 hour and up to 1 week before serving. Once refrigerated, allow to come to room temperature before serving.