“Jett” Black spinel ring, in a gorgeous Art Deco design.

Art Deco inspired black spinel ring.
Black spinel is a natural gemstone that is very under-utilized in ring designs. It is often mistaken for black diamond. However, whilst not quite as hard as a diamond, it has a far better polish and is usually without any fault lines (unlike black diamonds, which are usually full of faults, particularly in larger stones).
Its cost is relatively low compared to diamonds, which means very large stones are often in budget for most people.
Unfortunately, they are not available in large quantities in the supply line, mainly because many people do not know of the existence of this particular gemstone. It remains a great option if you like the jet black look.