The second is the abundance of volcanic glass, because the lava fragments are quickly cooled by water before crystals can form. Glass is a geologically unstable material. It alters rapidly to brownish-yellow clays, giving Molokini its earthy yellow color. In contrast, cinders erupted on land are reddish and black. For those dying to know, the Molokini deposits are basanite, a type of basalt with fairly low amounts of silicon and high concentrations of sodium and potassium.
Visible crystals are sparse, even under a magnifying glass.
Lava like this is typical of Haleakala's flows erupted during the past 500,000 years. The ocean near Molokini is a popular skin-diving location reached easily by boat. The island itself is off limits, however, because it serves as a bird sanctuary. We at the Hawaiian Volcano Observatory take this opportunity to thank Drs. The trip to Molokini was made possible through the expert piloting of Chief Petty Officer Robert Schmidt and Petty Officer Richard Maga a of the U.S. Coast Guard.