Determining the "hardest" igneous rock is tricky, as hardness is a measure of a material's resistance to scratching. This can be measured using the Mohs Hardness Scale. However, igneous rocks are complex mixtures of minerals, each with its own hardness.

Here's the thing:

* No single igneous rock has a definitive hardness. The hardness will vary depending on the specific mineral composition of the rock.

* Some minerals common in igneous rocks are very hard, like diamond (Mohs hardness 10), quartz (Mohs hardness 7), and feldspar (Mohs hardness 6). If an igneous rock is rich in these minerals, it will be relatively hard.

* Other common igneous minerals, like olivine and pyroxene, are less hard (Mohs hardness 6-7). A rock rich in these minerals will be less hard overall.

Therefore, it's more accurate to say that:

* Rocks like granite and rhyolite, which are typically rich in quartz and feldspar, are relatively hard.

* Rocks like basalt and gabbro, which are typically richer in olivine and pyroxene, are less hard.

Ultimately, the hardness of an igneous rock depends on the specific mineral composition and proportions of the rock.