I don't understand the confusion over this and desert flying. Sand in the desert is made of large grains of silica. They are rounded from years of abrasion and they won't have the same melt characteristics of the finer, sharper mica in the ash cloud, which being fine will melt more readily, will be deflected less by airflow direction changes (coating more of the engine interior) and being more abrasive.
These comparisons with sand storms are pointless. The differences in effects between mica and silica have been posted previously, which is where I learnt about them yesterday. I think many would benefit from reading the thread properly and learning form the scientists and engineers who have contributed.