Stone Flower or better known as Dagad Phool in India is a soft, brown and black colored lichen. The spice is used in many popular Indian dishes. I have not been able to locate them in Indian ethnic groceries in US and hence got my stash from one of my generous Paachis from India. These are available in specialty grocery chains in India. I also found them at exclusive spice and condiments store.
This spice is used for making various masalas like Goda Masala/ Kala Masala. It does have a strong earthy aroma and a very dry, light fluffy texture and feel to it. All said and done, no Marathi masala preparation process would be complete without these. The spice gives the signature black color to the masala. I recall a certain Maushi once refused to prepare her Kala Masala till she found Dagad Phool!! For more reference and better understanding of Marathi/ Maharashtrian cuisines, I found Ruchira - By Kamlabai Ogle very handy; a useful 2 book compilation originally written in Marathi dissecting and exploring the basic Marathi Amtis, Usals et al. Now, the English version is also available which makes it easier for anybody to explore the nuts and bolts of Marathi cuisine.