Exercises: Minerals and rocks

Explain the difference between a mineral and a rock, and give an example of a rock made of several minerals and another of a rock made almost entirely of a single mineral.

State three physical properties used to identify minerals in a laboratory practical and describe how each one is tested.

Name the three main types of rock based on their origin and summarise in one sentence the process that forms each type.

Arrange these processes and materials from the rock cycle into a cycle, explaining each transition: sedimentary rock, magma, metamorphic rock, igneous rock, sediments.

Classify these rocks as igneous, sedimentary, or metamorphic, and justify each classification based on its origin or texture: granite, sandstone, marble, basalt, slate, and limestone.

Observe the three numbered rock samples in the image. a) Describe the texture visible in each one (grain size, presence of strata or mineral bands). b) Relate each texture to the process that originated that type of rock. c) In which of the three would fossil remains be most likely to be found? Reason your answer.

During a survey in a volcanic-plutonic complex, three samples (A, B, and C) with identical rhyolitic/granitic chemical composition are analyzed:

• Sample A: millimeter-sized interconnected quartz, potassium feldspar, and biotite with no glassy or microcrystalline matrix.

• Sample B: homogeneous glassy mass and conchoidal fracture, showing no X-ray diffraction signals of crystal lattices.

• Sample C: angular feldspar phenocrysts embedded in a microscopic groundmass with small vesicles.

1. a) A preliminary report states that the textural differences are due to variations in the concentration of silica and water in the original magma. Refute this statement, justifying which is the actual physical variable responsible.
2. b) Reconstruct the cooling history (variation of the rate of heat loss over time) of each sample and deduce in which geological setting or emplacement (deep magma chamber, shallow dike, or surface lava flow) each one solidified.
3. c) Predict what texture a sample D will exhibit if it is collected right at the contact plane between the deep intrusion and the cold host rock.

The layout of a highway is planned to dismantle a slope where an inverted stratigraphic sequence with dinosaur tracks and continuous fossil ripples outcrops. The construction company requests to cover the slope in concrete, claiming that "the photographs already taken are sufficient as a record and the rock cut lacks practical utility."

1. a) Assess the uniqueness and fragility of this outcrop by applying the assessment criteria for Geosites (scientific, educational, and sociocultural value).
2. b) Refute with geological and methodological arguments the construction company's claim that photographic documentation replaces the in situ conservation of the outcrop.
3. c) Design an integrative technical proposal that ensures the geotechnical stability of the highway cutting while simultaneously allowing the preservation of the stratum and its use for safe educational itineraries.

Relate the dominant rock type to the landscape it shapes in these Mexican cases: the limestone formations of the Huasteca Potosina, the granite tors of La Rumorosa, and the volcanic tuffs of the Sierra de Órganos. Indicate which external process acts differently on each rock.