Question

Sample ${\mathrm{S}}_5$ has the following characteristic: a. effervesces in diluted $\mathrm{HCl}$ acid b. weakly effervesces in diluted HCl acid if powdered c. contains fossil shells and effervesces in diluted HCl acid d. contains pebbles and finer sediments e. a sooty or shiny appearance

Short answer

Sample ${\mathrm{S}}_5$ is likely a fossiliferous limestone.

Step-by-step solution

Analyze Effervescence in Diluted HCl Acid

Identify which statements relate to how Sample ${\mathrm{S}}_5$ reacts with diluted $\mathrm{HCl}$ acid. Statements a, b, and c discuss effervescence when exposed to $\mathrm{HCl}$. Effervescence typically indicates the presence of carbonates, such as calcium carbonate.

Examine the Physical Description

Statement d mentions the presence of pebbles and finer sediments. Statement e describes a sooty or shiny appearance. Together, these suggest a mixture of mineral particles with possible organic material or specific minerals like mica or coal.

Deduce Geological Characteristics

Effervescence in diluted $\mathrm{HCl}$ and the presence of fossil shells as noted in point c are indicative of limestone, specifically a fossiliferous limestone. The appearance of pebbles and finer sediments may indicate a sedimentary environment.

Identify the Rock Type

Consider all characteristics: effervescence with diluted $\mathrm{HCl}$, presence of fossil shells, pebbles, and finer sediments, and shiny appearance. Together, these suggest that Sample ${\mathrm{S}}_5$ is a limestone, possibly containing calcite and other mineral impurities or coal.

Key concepts

Effervescence in Geology

Effervescence is a fascinating chemical reaction in geology that occurs when certain minerals, particularly carbonates, react with acids. When you drop diluted hydrochloric acid ($\text{Math input error}$) on a rock sample and see bubbles or fizz form, it's called effervescence. This reaction happens because the acid breaks down the carbonate minerals, releasing carbon dioxide gas.
It's like a natural, mini volcanic eruption occurring on a microscopic level.

• This bubbling effect is a strong indicator of carbonate minerals being present in the sample.
• Common carbonate minerals include calcite and dolomite.
• Effervescence is often used to test quickly for limestone, which is rich in calcium carbonate.

This simple reaction helps geologists identify and differentiate types of rocks based on their chemical composition.

Limestone Identification

Identifying limestone in the field is a practical skill geologists often use. Limestone is primarily composed of calcium carbonate ($\text{Math input error}$) and readily reacts with diluted $\text{Math input error}$, producing a visible, effervescent reaction.
Different types of limestone can exist, with some containing fossilized shells or skeletal fragments, known as fossiliferous limestone.

• Limestone's reaction with acid is immediate and vigorous when the sample is directly exposed to $\text{Math input error}$.
• If limestone effervesces only weakly when powdered, it may contain mineral impurities that dilute the reaction.
• Fossiliferous limestone contains recognizable fossils, making it easy to spot in sedimentary layers.

By understanding these characteristics, geologists can confirm the presence of limestone in various geological settings.

Sedimentary Rock Analysis

Sedimentary rocks, like the sample possibly identified in our exercise, are formed from particles or sediments that compress over millions of years. These rocks can tell stories about Earth's past environments and conditions.
Analyzing sedimentary rocks involves examining grain size, composition, and sedimentary structures to interpret the rock's origin.

• Rocks containing pebbles suggest deposition in high-energy environments like rivers or beaches.
• Finer sediments, such as sand or silt, indicate quieter settings like lakes or deep marine basins.
• The presence of fossils within sedimentary rocks can indicate past life and environmental conditions.

By examining these features, geologists can reconstruct ancient landscapes and understand past climatic conditions.

Mineral Identification

Mineral identification is crucial in geology for understanding Earth's crust and resource potential. Identifying minerals in a rock sample involves a series of tests and observations based on physical and chemical properties.
This process can include visual inspection and testing chemical reactions, like effervescence.

• Physical properties such as color, luster, and hardness are often assessed first.
• Effervescence helps in identifying carbonate minerals like calcite.
• Additional tools, like microscopes and acid tests, provide more detailed insights into mineral composition.

Accurately identifying minerals leads to understanding a rock's history and formation processes.

Carbonate Minerals in Geology

Carbonate minerals play a significant role in geology as they are key components in many rocks and geological processes. Mainly composed of carbonate ions ($\text{Math input error}$), these minerals include calcite, dolomite, and aragonite.
They are major constituents of rocks such as limestone and dolostone.

• Calcite ($\text{Math input error}$) is the most common carbonate mineral, often tested through effervescence.
• Dolomite ($\text{Math input error}$) reacts weakly with $\text{Math input error}$ and is found in dolostone.
• Carbonates form in various environments, like ocean beds and evaporative basins.

These minerals are pivotal in understanding sedimentary rock formation and can influence climate change through carbon cycling.