marcasite is actually white iron pyrite (related to but not the same as pyrite-i.e. fools gold)
"Marcasite" is a natural stone that is set in jewelry after it is cut and polished.
90% jewelry is made from natural stones
it is jewelry that is made from natural resources like wood and stone
Yes, iron stone found in red and black banded form is called tiger iron is used in jewelry.
Jasper is a stone used in jewelry. It comes in many colors including blue, red, orange, black, brown, green, gray, or yellow.
Personally my wife loves turquoise jewelry. It is both inexpensive and attractive. Many times you will find that this jewelry is hand made which is an added bonus in my opinion.
The value of the stone(s) depends on the cut, natural colour, carat weight and clarity of the stone. A gemologist who is expert in black diamonds can help you value the stone(s).
It sounds like you have natural stone. Unfortunately if your black tiles are a natural stone like slate, you have etched your tile. Vinegar is an acid and works wonders on glazed tile, but natural stone will actually start to break down. I have heard that some contractors can sand or buff out the damage. Get in touch with a natural stone specialist. I would stop trying to get the white out until you get a pro out to tell you for sure.
stone
Quartz
Sapphire
Yes, stone is a natural substance, not man-made.