What was the literal meaning of the term 'stone rejected by builders'? Matthew 21:42 (NASB) says:


  Jesus said to them, “Did you never read in the Scriptures, ‘The stone
  which the builders rejected, This became the chief corner stone; This
  came about from the Lord, And it is marvelous in our eyes’?


I am curious to know the literal meaning of the expression, 'The stone which the builders rejected '. I wish to know what  qualities of the stone would be tested by the  masons of Jesus' time in order to assess its suitability for being used for construction. Which were the implements that enabled the testing ? 

Views of any denomiation are welcome.
While this is not a biblical source, according to an article on the Freemason website yorkriteofcalifornia.org, 

Foundation Stones, Cornerstone Ceremonies and other Masonic Stones

Submitted by Jerrold A. Wohlfarth
Grand High Priest 2007/2008
Grand Chapter of Royal Arch Masons of California

the following is said of a cornerstone in ancient times:

"We know that the cornerstone, or foundation stone, of an edifice in ancient times was a perfectly squared stone from which the remainder of the building could be plumbed, squared and leveled. It provided the builder a point of departure, or reference, which insured that the structure would be properly built. If the first stone, the foundation stone, or cornerstone was not plumb, square, and level, the error would become more and more exaggerated the further the builder went from that corner stone. We know that examination of still standing structures built in ancient times disclose the perfection and exactness required of the stonemasons who constructed the buildings of the time. The stones had to be perfect."

While this does not say anything about the composition of the stone it does address it's attributes and Masons would certainly be a good source of information.