Final answer:
Cleavage in minerals is identified by planar surfaces that reflect light and have predictable breaks along weak chemical bonds, while fracture is characterized by irregular and uneven breakage patterns. To determine which characteristic a specimen exhibits, one must closely examine the surface with a hand lens or light reflection to see if the breakage is planar (cleavage) or irregular (fracture).
Step-by-step explanation:
In geology, identifying the characteristics of minerals is crucial for understanding their properties and the geologic history of the rocks they comprise. Minerals may exhibit either cleavage or fracture, each indicating different structural tendencies within the mineral. Cleavage refers to the tendency of a mineral to break along flat, planar surfaces, which are the result of weak chemical bonds in certain directions. These cleavage planes may appear as shiny, reflective surfaces, especially when a light is shone on the mineral or when viewed with a hand lens. Recognizing cleavage can also involve considering the angle between cleavage planes, with some minerals having one, two, or multiple planes of cleavage.
On the other hand, fracture describes the way a mineral breaks with irregular, uneven surfaces. Unlike cleavage, fracture does not occur along planes of weak bonding but instead results in surfaces that do not have a clear, flat, or smooth appearance. A close examination with a hand lens or using light reflection can help distinguish between cleavage and fracture. This distinction is especially important when differentiating minerals with similar physical properties, such as amphibole and pyroxene, which differ in their cleavage properties.
A specimen that exhibits clear, planar surfaces that reflect light well and have a predictable break along these planes is likely a specimen with cleavage. Conversely, a specimen without a patterned breakage and showing irregular surfaces is an example of a specimen with fracture. To correctly identify the specimen as indicated by your instructor, look closely at the surface for these characteristics using the methods described.