Dear Curious -
To interpret the meaning of a dream, you must allow yourself to free-associate on its symbols: In particular, what do the black, egg-shaped, mineral stones remind you of? Is there any specific recollection or memory that is jogged by your contemplation of them? How did they make you feel in the dream? Why do you think they were minerals? Why do you think they were egg-shaped?
Eggs are powerful symbols. They indicate creation and creativity. That you were excited and considered them a great discovery is significant. An obvious interpretation of this dream might be that you are contemplating bearing children yourself. You were hiking in a lush forest with a man you do not know. The rhythmic activity of riding a horse, which occurred later in the dream, also can be interpreted sexually, as can the symbol that you were riding “a rope.” The fact that the eggs were found contained within the body of another stone, like the eggs stored in a woman’s body, also indicates fertility. However, I would hesitate to think that this dream is only about literal pregnancy. You may be enjoying a creative period within yourself. In this sense the dream indicates personal growth and discovery and self-expression. Congratulations!