The main differences between natural and lab-grown diamonds are their origin, formation process, and cost. Here are some of the key differences: 

1. Origin: Natural diamonds were formed deep within the Earth's mantle, while lab-grown diamonds are created in a laboratory setting. 
   
2. Formation process: Natural diamonds are formed over billions of years through a process of high pressure and temperature deep within the Earth's mantle, while lab-grown diamonds are created through one of two methods: High Pressure High Temperature (HPHT) or Chemical Vapor Deposition (CVD). Since laboratory-grown diamonds are created using modern technology, the oldest lab-grown diamond is only a few decades old. The first commercially successful production of synthetic diamonds began in the mid-1950s. While there may be lab-grown diamonds that are several decades old, it is unlikely that any lab-grown diamond would be considered "old" in the same way that natural diamonds can be dated back billions of years. 
   
3. Appearance: Natural and lab-grown diamonds can be visually identical to the naked eye, but there are differences that can be detected under magnification. For example, natural diamonds may contain inclusions or blemishes that are not present in lab-grown diamonds. Vice versa, the lab grown diamonds might exhibit growth lines, also known as "grain lines" or "growth striations." These lines are visible under magnification and are caused by changes in the growth conditions or crystal structure during the diamond's formation process. These growth striations can sometimes be used to identify lab-grown diamonds, as they are not typically found in natural diamonds. However, the presence of growth striations does not necessarily indicate that a diamond is lab-grown, as natural diamonds can also rarely exhibit similar growth features. For more informations on microscopic features of diamonds, visit https://www.gia.edu/gems-gemology/winter-2018-inclusions-natural-synthetic-treated-diamond 
   
4. Cost: Lab-grown diamonds are typically less expensive than natural diamonds, although prices can vary depending on the size, quality, and other factors. 
   
5. Rarity: Natural diamonds are rare and valuable due to their limited supply and the difficulty of extracting them from the Earth, while lab-grown diamonds can be produced in larger quantities and more consistently.