There are 13 words that start with 'petrog'.
| petrogeny | petroglyph |
| petrogenies | petroglyphs |
| petrography | petrogeneses |
| petrogenesis | petrogenetic |
| petrographer | petrographic |
| petrographers | petrographies |
| petrographical | |
Note: These 13 words that start with 'petrog' are found from the USA & Canada version of the tournament Scrabble word list.