ROCKS, MINERALS, AND OTHER STUFF   Developing this key is going to be a challange. The purpose is to cover those things found in aquatic environments in Hawai‘i that are NOT living (Or, in some rare cases, things that may not appear to be the result of biological activity, but in fact are). Some such "oddities" are covered already on the preliminary key page and you may wish to start there with couplet 2. The rest will be dealt with starting here. The purpose is to provide a systematic approach to naming the materials that make up the features seen in an aquatic environment. Attempting this part of the Key to Aquatic Organisms (and now Features!) is encouraged by the fact that a serviceable key to rocks and minerals is available on the internet (The Rock Key by Donald Peck), suggesting at least one approach that might be of some use here. This key will go as far as reasonable descriptions can be developed for the components of the physical features encountered in aquatic environments, and hopefully provide an enjoyable exercise for students wishing to practice using a key to identify something. A magnifying lens will be helpful (perhaps, required).

First, some concepts and definitions. The key assumes you are attempting to name a "specimen"—that is, something you have in hand or could have in hand, having collected or observed it in an aquatic environment in the Hawaiian Islands. That something may be hard (a "rock") or soft (composed of small grains), or perhaps even squishy; but it is not obviously part or all of a living organism. Rocks are the solid substance of the earth, but are eroded by various processes into smaller and smaller particles that we can call grains (once they are too small to be rocks anymore). Solid rocks at the earth's surface break down—through physical and chemical actions over a long time—into softer formations that we might term soils. In other cases, the small pieces eroded from the rock—small rocks and grains—are moved by gravity, wind, or water and collect as deposits. Aquatic environments, representing accumulated water on the earth's surface, can be agents in erosion (as in a flowing stream moving and breaking up rocks into smaller pieces) or places of deposition (as at the bottom of a pond, lake, or estuary, or even slow moving parts of a stream).

The three basic categories of rocks are: igneous, sedimentary, and metamorphic. Igneous rocks are the result of magma cooling on or near the surface; they are formed by volcanic activity. Obviously, the vast majority of rocks in the Hawaiian Islands are igneous rocks. Sedimentary rocks form where deposits of small grains bind together and harden back into rock. In Hawai‘i, sedimentary rocks are the result of a cementing process from substances dissolved in water "glueing" the grains together. Metamorphic rocks are former igneous or sedimentary rocks that have undergone a change in composition, typically a result of being subjected to great heat and pressure when buried deep in the earth. However, the heat from volcanic activity can also produce changes in the surrounding igneous rocks that classify these as metamorphic.

Rocks and grains are composed of minerals. Surprisingly, there are not all that many common minerals that make up rocks, and the rocks and minerals in Hawai‘i are not nearly so diverse as those to be found on the world's continents.

	15a		Specimen is, or at least is like, a rock: hard and very solid and at least 1/4-inch across	[16]
	15b		Specimen is soft, presumably composed of many small grains that may or may not be visible (most are smaller, maybe much smaller, than 1/4-inch across)	[100]
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	16a	(3)	Specimen is a rock/mineral with crystaline structure (a crystal) OR has inclusions that are crystals (typically, small, flat, shiny surfaces)	[17]
	16b		Specimen lacks any evidence of crystals, even under magnification	[100]