Final answer:
Color, hardness, and density are unreliable physical properties when identifying minerals in the absence of scientific instruments.
Step-by-step explanation:
The unreliable physical properties that must be used cautiously when identifying minerals in the absence of scientific instruments are color, hardness, and density.
Color: The color of minerals is not a reliable indicator because different minerals can come in various colors. For example, quartz can come in different colors.
Hardness: While hardness can be used to identify minerals, it is not always unique. Some minerals have similar hardness, making it necessary to use additional properties for accurate identification.
Density: Density can vary for different minerals, but it is not a definitive indicator since some minerals can have similar densities.