Learn Italian: L'isola minore ha il cratere con il diametro minimo. - The minor island has the crater with the minimum diameter.

Both are grammatically correct! Minore is the irregular comparative of piccolo (small). In everyday speech, più piccola (smaller) is common, but minore is often used for established names, like geographical features (the minor island) or for age (younger sibling).

What is the exact difference between minore and minimo in this sentence?

Minore is the comparative form (smaller or minor), comparing this island to a larger one. Minimo is the absolute superlative form (smallest or minimum). It describes the crater's diameter as being the absolute smallest possible, rather than just comparing it to one other specific crater.

Why doesn't minore change its ending to match the feminine noun isola?

Because minore ends in -e, it follows the standard rule for Italian adjectives ending in -e: they use the same ending for both masculine and feminine singular nouns. It only changes in the plural, where it becomes minori.

How do we know the gender of cratere since it ends in -e?