There is (dry) rock often used as base rock, (wet) base rock which is sold out of a tank and has bacterial life but is usually with out any visible surface life, and live rock which has both bacterial life and at least some surface life such as coralline algae and maybe more. Dry base rock can be bought for about 50 cents a pound and up. Wet base rock is typically half the cost of fair live rock or a third the cost of good live rock. Of course that varies from store to store. It is always best to cure live rock before adding it to an already cycled tank if fish and coral are in the tank that will house the new coral. Of course you can take chances, and hopefully learn by them. The benefit of live rock is in both the bacteria and all the other life forms that come along with good live rock. Usually even wet base rock supplies virtually no other live forms but bacteria, and dry base rock supplies no bacteria or other life forms. If starting a tank with base or dry rock other life forms must be imported in order for them to exist in a tank, they do not just materialize out of air or come from a bottle. It is always best to inoculate your new tank with some quality live rock and live sand. Even if only 5 to 10 percent of your rock and sand is quality live rock and live sand it makes a huge difference in your tanks ultimate health. Especially if you want your tank to mature in a timely fashion. Even then a tank is usually not considered fully mature for a year or more.
