Today's Moissanite Passes a Diamond Tester due to it's similar hardness and refractive index (the sparkle) of a top quality diamond. You can't tell the difference.
Moissanite is a natural material with a background that’s almost too incredible and mysterious to believe. The stone was first discovered in tiny fragments at the site of a meteor impact in an Arizona desert. The French scientist that discovered it thought the specimen was diamond for many years. Eventually, its true nature was discovered. Moissanite is incredibly hard, in fact, the only stone that’s known to be harder is diamond. That made synthetic Moissanite a great (and more affordable) choice for many industrial applications (like industrial abrasives).
When it comes to Moissanite being tested as a diamond, the two have very similar qualities. This makes it very hard to tell the difference between diamonds and moissanite, even with using a diamond tester. In the past few years, technology involving moissanite has advanced greatly, allowing for it to be truly colorless. It has a beautiful diamond-like appearance and durability but costs 90% less than the average diamond. It conducts heat very similar to a diamond which is the main test used in a diamond tester, allowing for most moissanite to oftentimes pass as a diamond. Typically, a diamond tester will register both moissanite and diamond as a diamond!