In geology, which one of the following statements is NOT true according to the standard definition of a mineral?

Introduction / Context:
Minerals are the building blocks of rocks and are fundamental to the study of geology and earth science. The standard definition of a mineral includes several key characteristics, such as being naturally occurring, inorganic, solid, and having a definite chemical composition and crystalline structure. This question asks you to identify which statement about minerals does not fit this accepted definition and is therefore not true for minerals in the strict scientific sense.

Given Data / Assumptions:

• The statements refer to properties of minerals as understood in geology.
• Key aspects of the mineral definition include physical state, structure, and composition.
• The options suggest that minerals might be liquids, solids, or glasses, and refer to chemical composition and internal structure.
• We assume the widely accepted textbook definition of a mineral.

Concept / Approach:
A standard definition of a mineral is: a naturally occurring, inorganic, solid substance with a definite, but sometimes variable, chemical composition and an orderly internal crystalline structure. This definition excludes liquids and non crystalline materials such as ordinary glass. Minerals are identified by their characteristic physical properties, including hardness, cleavage, colour, lustre, and density, which reflect their internal structure and composition. Therefore, any statement that allows minerals to be liquids or glasses contradicts the definition and must be false, while statements about specific physical properties, crystalline structure, and predictable composition are true.

Step-by-Step Solution:
Step 1: Recall that minerals must be solids at standard Earth surface conditions to fit the strict definition. Step 2: Recognise that minerals are crystalline, meaning their atoms are arranged in an orderly, repeating pattern. Step 3: Understand that minerals have a specific chemical composition that may allow for limited substitution but remains predictable. Step 4: Identify that minerals can be identified by physical properties such as hardness, cleavage, and density, which are characteristic and reproducible. Step 5: Note that the statement claiming minerals can be a liquid, solid, or glass directly contradicts the requirement that minerals are solid and crystalline, making this statement not true.

Verification / Alternative check:
Geology textbooks and reference materials emphasise that glass (such as volcanic glass obsidian) is not a mineral because it lacks a long range crystalline structure, even though it may be naturally occurring and solid. Similarly, liquids like water are not considered minerals under the strict definition, although ice, the solid crystalline form of water, is classified as a mineral. These examples highlight that only solid, crystalline forms meet the mineral definition. Therefore, any statement suggesting that minerals can be liquids or glasses is inconsistent with this widely accepted view.

Why Other Options Are Wrong:
The statement that minerals can be identified by characteristic physical properties is correct; these properties derive from their composition and internal structure. The statement that minerals have a specific internal crystalline structure is also correct and is part of the core definition. The statement that minerals have a specific, predictable chemical composition is true, although some minerals allow limited chemical substitution; overall, their composition falls within a defined range. These statements all align with the standard definition, so they cannot be the incorrect one the question is asking you to find.

Common Pitfalls:
Students sometimes confuse the broader term natural material with the more precise term mineral and may think that any naturally occurring substance, including liquids and glasses, qualifies as a mineral. Another pitfall is to focus only on composition and forget the requirement of crystalline structure and solid state. To avoid these errors, memorise the key points of the mineral definition: naturally occurring, inorganic, solid, crystalline, and with a definite chemical composition. With those criteria in mind, it becomes clear that liquids and glasses are excluded from the mineral category.

Final Answer:
The statement that is NOT true for minerals is: they can be a liquid, solid, or glass, because minerals must be solid and crystalline under the standard definition.