Moissanite is a naturally occurring material and is simply a combination of silicon and carbon. While it was first discovered in meteor in the late 1800's, it is extremely rare and is now produced in a lab. It is the second hardest material on Earth (rating a 9.5 out of 10 on the Mohs hardness scale) and is double refracted, letting off even more sparkle and brilliance than diamond.
While they may look very similar to the naked eye, Moissanite is not the same type of stone as diamond and differs in many ways from it. For one, Moissanite is a combination of silicon and carbon, whereas diamond only contains carbon. Moissanite is also double refracted and lets off a more brilliant sparkle, compared to diamond which is only single refracted. Moissanite is made in a lab, allowing for strict and repeatable quality control, without the environmental and humanitarian impacts of diamond mining.
Yes, Moissanite is an excellent option for engagement or wedding rings. It is very durable, requires minimal maintenance, and shares many of the benefits of diamond in that regard. However, Moissanite is lab-made and doesn't come with the environmental and humanitarian drawbacks of diamond mining. It is also much more affordable, often costing 5-10x less when comparing to a diamond of a similar color, clarity, and carat.
Moissanite is a very durable and stable material, requiring minimal maintenance over many years. However, as with most gemstones, Moissanite and its gold setting can accumulate dirt or debris over time. Moissanite can be cleaned the same way you would clean any other fine gemstone. An ultrasonic cleaner can be used, but it is important to always be as gentle as possible with treasured items. A commercial (non-acid based) jewelry cleaner, or mild soap, water, and a soft toothbrush may also be used. A Sunshine Polishing Cloth may be used to remove any organic film or haze that may build up over time.