An anonymous reader writes with this quote from a NASA press release:
"Tiny crystals of a green mineral called olivine are falling down like rain on a burgeoning star, according to observations from NASA's Spitzer Space Telescope. This is the first time such crystals have been observed in the dusty clouds of gas that collapse around forming stars. Astronomers are still debating how the crystals got there, but the most likely culprits are jets of gas blasting away from the embryonic star. ... The crystals are in the form of forsterite. They belong to the olivine family of silicate minerals and can be found everywhere from a periodot gemstone to the green sand beaches of Hawaii to remote galaxies. NASA's Stardust and Deep Impact missions both detected the crystals in their close-up studies of comets. ... The findings (abstract) might also explain why comets, which form in the frigid outskirts of our solar system, contain the same type of crystals."