HAJAR AL-ASWAD (BLACK STONE)
The Black Stone (الحجر الأسود) near Kaba, Makkah, in Arabic, is called Al-hajar Al-aswad. Many geologists and historians believe it to be a meteorite. It is the eastern cornerstone of the Kaba, the ancient sacred stone building towards which Muslims pray, in the center of the Grand Mosque in Makkah, Saudi Arabia. The Stone is a dark rock, polished smooth by the hands of millions of pilgrims that has been broken into a number of fragments cemented into a silver frame in the side of the Kaba. 
After Abraham (Peace be upon Him) finished erecting the Kaba, one rock was missing (in order to complete the Kaba) so he asked Ishmael to look for a rock. He searched and upon returning he found that his father had placed a rock. So he asked his father: 'O father where did you get this rock from?' He said: 'Gabriel brought it to me from the Heavens.'
And they completed the erection of the Kaba. When this rock was sent down from the heavens, it was whiter than milk. The Prophet said: 'The Black Stone was sent down from the heavens whiter than milk and it was blackened by the sins of man.' Tirmidhi 2577 (Ref. in Arabic 877)
When the Quraysh demolished the Kaba in order to reconstruct it, a dispute arose when the building reached the level of the Black Stone. They differed on the issue of who was eligible to restore the Black Stone to its original place. A civil war was about to break out. Banu Abdu’d-Dar brought a bowl full of blood and all of the tribes inserted their hands in it, which meant that they had made up their minds to fight one another. But Abu UmayyaIbn al-Mugheera , their elder, asked Quraysh to agree on the judgment of the first person to come through the BaniShaibah gate and they all agreed on this suggestion. The first to come through this gate was the Prophet (May Allah honour Him and grant Him peace). This was five years before his mission. He put the Black Stone in the middle of a piece of cloth, and asked a representative of each tribe to hold one of the edges of the cloth and raise it close to its place. Then the Prophet (May Allah honour Him and grant Him peace) picked it up with his own noble hands and restored it to its original place. This was how the Prophet (May Allah honour Him and grant Him peace) prevented a war from breaking out among the Quraysh by a supreme demonstration of wisdom.
Ibn Abbas (R.) relates that the Prophet (May Allah honour Him and grant Him peace) while leaning against the Kaba said: “The Hajr al-Aswad and al-Maqam (Ebrahim) are two jewels from the jewels of Paradise. Had a (Glory be to Him) not concealed their radiance, they would illuminate everything between the East and the West.” [Tirmidhi]
The Hajar al-Aswad was stolen from the Kaba around 930 CE by Qarmatian warriors who were an Ismaeeli Shia sect. They sacked Makkah, desecrating the Well of Zamzam with Muslim corpses and carried the Black Stone away to their base in Ihsaa, in medieval Bahrain. According to the historian Al-Juwayni, the Stone was returned in around 952 CE and restored to its original location.
The Hajar al-Aswad was originally a complete stone but due to various historical incidents now consists of eight pieces of varying sizes affixed to a large stone and encased in a silver frame. The silver frame was first made by Abdullah bin Zubayr (May Allah be pleased with Him) and replaced by later Khalifas as the need arose.
Six (additional) pieces are claimed to be in Istanbul, Turkey. One is displayed in the mihrab of the Blue Mosque, one above the entrance of the tomb of Sulaiman the Magnificent and four in the one over the mihrab, one below the lower pulpit, another is above the upper pulpit and the last is over the entrance door. The authenticity of these additional pieces has been questioned, although the Turks did rule over what is now Saudi Arabia for many years and hold many historical Islamic relics. And Allah (Glory be to Him) knows best.
It was narrated that Abu Tufayl said: "I saw the Messenger of Allah [PBUH] performing Tawaaf around the House, touching the corner [where the Stone is] with a crooked staff which he had with him, then kissing the staff." Sahih Al Muslim, 1275
It was narrated that Ibn ‘Abbaas said: The Messenger of Allah [PBUH] performed Tawaaf on his camel, and every time he came to the corner [where the Stone is] he would point to it and say “Allahuakbar.” Sahih Al Bukhari, 4987
According to a hadeeth narrated by al-Tirmidhi and others, it came down from Paradise, but there is some weakness in the isnaad of this report… the hadeeth was narrated by al-Tirmidhi and classed as saheeh by al-Albaani in Saheeh al-Tirmidhi, 695. 
There are a number of ahaadeeth etc. about the Black Stone which we will quote for our brother so that he may learn from them.
Although so reverently kissed and caressed during the Tawaf, the Black stone, in one of the corners of the Kaba, is no graven image for the pilgrims to worship. That is the last thing any One-God worshipper could ever imagine. For a stone is just a mere stone after all. It has no power whatsoever to do good or inflict harm to any one, apart from Allah, the Sole Deity of mankind. That is a thing cherished either knowingly, ignorantly or figuratively - by those who take to stone-worship instead of God-worship, a belief and practice as unholy as it is senseless. This is why the Black Stone becomes a mystery to such people, and so, some out of ignorance openly charge that Prophet Muhammad (May Allah honour Him and grant Him peace) did break every Idol in Islam except one - meaning the Kaba, or the Black Stone. Why, even unwitting Muslims get easily confused about the Black Stone. It was hence that 'Umar the second Caliph, did well to remove this hidden doubt from the mind. So when he came to kiss the Stone, he cried out publicly to it: Narrated 'Abis bin Rabi'a: 'Umar (R) came near the Black Stone and kissed it and said, "No doubt, I know that you are a stone and can either harm anyone nor benefit anyone. Had I not seen Allah's Messenger (peace be upon him) kissing you, I would not have kissed you. Summarized Sahih Al-Bukhari, 808
Kissing a stone is not a sign of its worship at all. Kissing the Black Stone cannot be twisted into an idol worship, for the stone is no image, just as mere kissing is not worshipping by a mere imagination. Anyone might allege that Muslims do worship a certain 'idol'. But the fact remains that they do not worship anything save God, the One. The idol and its worship simply do not exist.