Garnierite from near Riddle, Oreg., is an inhomogeneous material that has three general modes of occurrence. An orderly variation in the physical properties and chemical composition of eight analyzed specimens is a significant field guide for economic geologists examining nickel-silicate deposits. The NiO content of the specimens ranges from 2.6 to 37.0 percent. In general, the garnierite specimens rich in nickel are darker green than those poor in nickel and have a higher specific gravity, higher mean index of refraction, and different X-ray and differential thermal analysis patterns. Laboratory evidence supports the conclusion that the eight specimens are not variations of a single mineral but are mixtures of two or more hydrosilicates.