The Black Stone was described by European travellers to Arabia in the 19th- and early-20th centuries, who visited the Kaaba disguised as pilgrims. Swiss traveller Johann Ludwig Burckhardt visited Mecca in 1814, and provided a detailed description in his 1829 book Travels in Arabia:
It is an irregular oval, about seven inches [18 cm] in diameter, with an undulated surface, composed of about a dozen smaller stones of different sizes and shapes, well joined together with a small quantity of cement, and perfectly well smoothed; it looks as if the whole had been broken into as many pieces by a violent blow, and then united again. It is very difficult to determine accurately the quality of this stone which has been worn to its present surface by the millions of touches and kisses it has received.
It appeared to me like a lava, containing several small extraneous particles of a whitish and of a yellow substance. Its colour is now a deep reddish brown approaching to black. It is surrounded on all sides by a border composed of a substance which I took to be a close cement of pitch and gravel of a similar, but not quite the same, brownish colour. This border serves to support its detached pieces; it is two or three inches in breadth, and rises a little above the surface of the stone. Both the border and the stone itself are encircled by a silver band, broader below than above, and on the two sides, with a considerable swelling below, as if a part of the stone were hidden under it. The lower part of the border is studded with silver nails.
Visiting the Kaaba in 1853, Richard Francis Burton noted that:
The colour appeared to me black and metallic, and the centre of the stone was sunk about two inches below the metallic circle. Round the sides was a reddish-brown cement, almost level with the metal, and sloping down to the middle of the stone. The band is now a massive arch of gold or silver gilt. I found the aperture in which the stone is, one span and three fingers broad.
Ritter von Laurin, the Austrian consul-general in Egypt, was able to inspect a fragment of the Stone removed by Muhammad Ali in 1817 and reported that it had a pitch-black exterior and a silver-grey, fine-grained interior in which tiny cubes of a bottle-green material were embedded. There are reportedly a few white or yellow spots on the face of the Stone, and it is officially described as being white with the exception of the face.
i.e. Black Rock…etc… 
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