Final answer:
option b,Calcite is the mineral that cannot be scratched by a fingernail but can be scratched by a copper penny, placing it at a specific hardness on the Mohs scale between gypsum and fluorite.
Step-by-step explanation:
The student's question relates to the relative hardness of minerals and their identification through a simple scratch test, which is a common method in geology. Calcite is the correct answer to the question as it is a mineral that cannot be scratched by a fingernail, which implies it is harder than gypsum (which can be scratched by a fingernail), but can be scratched by a copper penny, indicating that it is softer than fluorite. It's crucial to note that the Mohs scale of mineral hardness is used to classify minerals based on their ability to scratch another mineral. Talc is the softest mineral on the Mohs scale and can be scratched by a fingernail. Dolomite is slightly harder than calcite and would not be as easily scratched by a copper penny.
The mineral that is not scratched by a fingernail but is scratched by a copper penny is calcite. Calcite is a mineral composed mainly of calcium carbonate. It has a hardness of 3 on the Mohs scale, which means it can be scratched by a copper penny (hardness of 3.5) but not by a fingernail (hardness of around 2.5).