The Black stone, an idol of worship in moon god pre-Islam time, is still worshipped by the Muslims and is described as follows:
The concept of the Black Stone is encrypted & symbolic, remember that a lot of mysticism is in involved here so things are not as plain as day. Kaaba meaning cube, is the foursquare of Mecca. A foursquare is a 'magic' square whose sides all equal a certain number, the particular one used by the ancient sages is here
http://mathworld.wolfram.com/MagicSquare.html
- Draw a line from the top of 1 to 4,then 4 to 2 another from 1 to 9 & another 6 to 2 you'll transcribe a marking that was/is on many buildings in the world, it was a map, so to speak, to the saying ' the 8 is the way to the 9', because you will notice after drawing those lines the only figure left out is 8, which symbolises perfection of symmetry. This utterence bewildered any not acquainted with such things but to someone who knew it was the key to another saying 'in the 9 heavens are 8 places', where is the 9th?
Double meaning abounds in that stone, for 9 in Arabic is Ta, which is also the Arabic root for "secret knowledge" There is a reason why it is black & not any other colour (hajarel aswad) black in Arabic root can be coal therefore this 'stone of black' or (hajarel fehm) is also "the stone of the wise" or "stone of wisdom".
This leads further into the derivative English word "cornerstone" which means
cor·ner·stone also corner stone
n.
A stone at the corner of a building uniting two intersecting walls; a quoin.
Such a stone, often inscribed, laid at a ceremony marking the origin of a building.
An indispensable and fundamental basis: the cornerstone of an argument.
You will hear many meanings as to the meaning of the the Black Stone, but the reason why the sufis used the foursquare & the sayings was so as to preserve the essence of its meaning....the 9 th heaven is in the heart.