Turquoise is a secondary mineral, meaning it forms from the alteration of other minerals. It is most commonly associated with igneous rocks, specifically those containing copper.

Here's how it works:

1. Igneous Rock Formation: The original rock is an igneous rock, often a volcanic rock like basalt or andesite, containing copper.

2. Weathering and Oxidation: The igneous rock weathers and oxidizes, releasing copper ions into the surrounding environment.

3. Hydrothermal Activity: Water, often enriched with phosphate and aluminum, interacts with the copper ions.

4. Turquoise Formation: Under specific conditions of temperature and pressure, the copper ions combine with phosphate, aluminum, and water to form turquoise.

Therefore, while turquoise is directly derived from igneous rocks, it is not itself igneous. It is a secondary mineral that forms due to the alteration of igneous rocks through weathering and hydrothermal processes.