18% at 25 mhttp://books.google.com.au/books?id=imMJJP5T5rsC&pg=PA231&lpg=PA231&dq=Salar+de+Atacama+and+porosity&source=web&ots=s2HzmWW8bt&sig=nJWp5_4wGnkes7s1j3TEzFujvJ4&hl=en&ei=KiGSSZ7KApWksAP3qLSsCw&sa=X&oi=book_result&resnum=1&ct=result