Matthew 16:18 - http://bible.cc/matthew/16-18.htm
Jesus said that Peter was *petros*(masculine) and that on this *petra*(feminine) He would build His church.
Greek: 4074 Pétros (a masculine noun) – properly, a stone (pebble), such as a small rock found along a pathway. 4074 /Pétros (”small stone”) then stands in contrast to 4073 /pétra (”cliff, boulder,” Abbott-Smith).
“4074 (Pétros) is an isolated rock and 4073 (pétra) is a cliff” (TDNT, 3, 100). “4074 (Pétros) always means a stone . . . such as a man may throw, . . . versus 4073 (pétra), a projecting rock, cliff” (S. Zodhiates, Dict).
4073 pétra (a feminine noun) – “a mass of connected rock,” which is distinct from 4074 (Pétros) which is “a detached stone or boulder” (A-S). 4073 (pétra) is a “solid or native rock, rising up through the earth” (Souter) – a huge mass of rock (a boulder), such as a projecting cliff.
4073 (petra) is “a projecting rock, cliff (feminine noun) . . . 4074 (petros, the masculine form) however is a stone . . . such as a man might throw” (S. Zodhiates, Dict).
It’s also a strange way to word the sentence that He would call Peter a rock and say that on this I will build my church instead of *on you* as would be grammatically correct in talking to a person.
There is no support from the original Greek that Peter was to be the rock on which Jesus said he would build His church. The nouns are not the same, one being masculine and the other being feminine. They denote different objects.
Interesting insight into the words themselves, and that appears to be exactly how Augustine is reading them as well:
“”For petra (rock) is not derived from Peter, but Peter from petra; just as Christ is not called so from the Christian, but the Christian from Christ.”
IOW, the “pebble” derives from the “rock,” which is Christ.