Memory Game Mixtures and Soil MemoryOnline version Match the vocabulary word to the definition. by Michael Porter a combination of two or more different substances that keep their identities clay Particles of rock that are smaller than sand but larger than clay the remains of decayed plants or animals in the soil The smallest particles of rock that make up soil mixture A mixture of water, air, tiny pieces of rock, and humus humus physical property weathering The upper layer of soil in which plants have most of their roots silt decay To be slowly broken down by the natural processes that destroy a plant or body topsoil The largest particles of rock that make up soil sand The breaking down of rocks on Earth’s surface into smaller pieces soil A characteristic of matter that you can observe or measure directly