Answer: Odor
Step-by-step explanation: "Odor" is not a characteristic that helps to classify rocks. Rock classification is based on the study of physical and chemical properties such as texture, mineral composition, and color. Odor is not considered to be a significant factor in rock classification, as it can be subjective and may change over time. The main characteristics that are used to classify rocks are texture (the size, shape, and arrangement of mineral grains), mineral composition (the types and proportions of minerals present), and color (the hue, saturation, and brightness of the rock's surface). These characteristics help geologists to identify the type of rock, its origin, and how it formed.