Lab grown diamonds have the exact same chemical and physical properties as a natural diamond. The only difference is one was grown in a machine in a matter of weeks while the other took between 1 billion and 3.3 billion years to form in the earth’s mantle. Both are made of carbon and will test as a diamond- because they both are!
Creating a lab diamond costs money, but significantly less than it takes to mine a natural diamond. Because of this, that difference in cost is passed along to the final retail of the diamond. Typically a lab grown diamond will cost 1/3-1/4 that of a natural diamond.
Because lab grown diamonds take significantly less time to produce, there really isn’t a resale value on the secondary market. They aren’t considered rare due to their abundance and availability versus a natural diamond. As science and supply chain advances, lab diamond pricing has continued to fall. This trend will likely continue- whereas the natural diamond market has stayed relatively steady over several decades.