Final answer:
The only difference between rose quartz, smoky quartz, and milky quartz is their color. They all have the same chemical composition and hardness, with color variations due to impurities and trace elements.
Step-by-step explanation:
The only difference between rose quartz, smoky quartz, and milky quartz is their color. All these varieties are forms of quartz and share the same chemical composition, silicon dioxide (SiO2), and hardness (7 on the Mohs scale of mineral hardness).
These types of quartz differ only in the impurities present, which give each type its distinctive color: pink for rose quartz, brown to black for smoky quartz, and white or milky for milky quartz. The presence of trace elements and irradiation are factors that influence the color variation in these minerals.