Streak

Definition

Streak refers to the color of the powder produced when a mineral is scraped across a streak plate, usually made of unglazed porcelain. This property is important in mineral identification because the streak can be more consistent than the color of the mineral itself, which may vary due to impurities or weathering. Streak provides a quick way to help distinguish between minerals with similar appearances and contributes to a better understanding of their composition.

5 Must Know Facts For Your Next Test

1. Streak is often tested by rubbing the mineral on a streak plate and observing the color of the resulting powder.
2. Some minerals have a different streak color than their external color; for example, hematite appears metallic gray but has a reddish-brown streak.
3. Streak is especially useful for identifying non-metallic minerals, where color can be misleading due to variations.
4. The streak test is simple and can be performed in the field or lab with minimal equipment, making it a practical tool for geologists.
5. While most minerals produce a streak that matches their color, some can yield an unexpected streak, emphasizing the importance of this property in identification.

Review Questions

• How does the streak of a mineral aid in its identification compared to its overall color?
  • The streak of a mineral often provides a more reliable indicator for identification than its overall color. This is because minerals may contain impurities that alter their external appearance, leading to color variations. By examining the streak color produced on a streak plate, geologists can gain insights into the mineral's true characteristics and differentiate between minerals that may look alike.
• Discuss how the properties of luster and streak work together in mineral identification.
  • Luster and streak are both crucial properties in the process of identifying minerals. Luster describes how a mineral reflects light, giving clues about its composition and potential classification as metallic or non-metallic. Meanwhile, streak reveals the true powder color regardless of surface imperfections. Together, these properties help refine the identification process by allowing geologists to narrow down possibilities when encountering unknown samples.
• Evaluate the significance of conducting a streak test in fieldwork and how it impacts mineralogical studies.
  • Conducting a streak test in fieldwork is significant as it allows geologists to quickly identify minerals on-site without needing extensive laboratory equipment. This immediate assessment can guide further investigation and sample collection based on initial findings. By using streak tests alongside other properties such as hardness and luster, researchers can create a more comprehensive profile of mineral samples, enhancing our understanding of geological formations and contributing to broader mineralogical studies.

Related terms

Mohs Hardness Scale: A scale that ranks minerals based on their ability to scratch one another, from 1 (talc) to 10 (diamond).

Luster:

The way a mineral reflects light, which can be described as metallic, glassy, pearly, or dull.

Cleavage:

The tendency of a mineral to break along flat planes of weakness in its structure.