Sea of Glass
"Though sand looks little like glass, most of the common glasses contain from 60 to 80 per cent sand by weight. And this material forms the skeleton about which the glass-forming process takes place."
"The chief raw material in the manufacture of glass is sand."
(Universal Standard Encylcopedia)
"By myself have I sworn, saith the LORD, for because thou hast done this thing, and hast not withheld thy son, thine only son: That in blessing I will bless thee, and in multiplying I will multiply thy seed as the stars of the heaven, and as the sand which is upon the sea shore; and thy seed shall possess the gate of his enemies; And in thy seed shall all the nations of the earth be blessed; because thou hast obeyed my voice." - Genesis 22:16-18