This is dark grey to black limestone, the black lines are organic matter (mainly lignin/cellulose from plants, which at that time couldn’t be broken yet by fungus). The limestone is oolithic (small round balls) which formed on a platform(like today’s Bahamas) when wave action causes repetitive action. The stone was slightly heated during lithification, which turned the organic matter into keratogene (stage prior to forming coal/oil) concentrated in thin layers.

Material can be finished (leather type) into a very hard, black surface. When used indoors it remains its beautiful black colour and texture, outdoors the ultraviolet will turn the black keratogene layers into grey over a number of years. Regular coating may slow down this process. Further large tiles always will curve slightly, so make sure that your supplier controls this issue. A joint of 1 to 2 cm is recommended to compensate for this problem