The siliceous geyserites of Yellowstone National Park (Wyoming, U.S.A.) are morphologically very similar to stromatolites, but are abiogenic. Geyserite is opaline silica deposited non-biogenically within and around hot springs and geysers. The deposits have a variety of shapes, each characteristic of particular environments. The shapes strikingly resemble those of stromatolites; however, the morphogenetic processes are non-biological. Columnar and spicular geyserite forms in subaerial splash zones; stratiform geyserite forms subaqueously; oolitic and pisolitic geyserites form in turbulent water, and may be continually or only intermittently submerged. Geyserite is distinguished from stromatolites by its distinctive distribution around points of water discharge, by microcrosslamination that is common but not ubiquitous, and by its banded lamination with laminae less than about 4μm thick. Spicular and columnar forms could have formed in many types of water-splash zones, such as along shorelines. The word stiriolite is introduced for geyserite-like deposits preserved in the geological record.