The third precious stone used in the foundation of the walls of the New Jerusalem (Rev. 21: 19), ‘agate’ (NRSV); perhaps crystallized quartz and silica.
Citation for chalcedony
Citation styles are based on the Chicago Manual of Style, 15th Ed., and the MLA Style Manual, 2nd Ed..
MLA
"chalcedony." In A Dictionary of the Bible. Ed. W. R. F. Browning. Oxford Biblical Studies Online. May 23, 2013. <http://www.oxfordbiblicalcstudies.com/article/opr/t94/e370>.
Chicago
"chalcedony." In A Dictionary of the Bible. , edited by W. R. F. Browning. Oxford Biblical Studies Online, http://www.oxfordbiblicalcstudies.com/article/opr/t94/e370 (accessed May 23, 2013).