The texture of an igneous rock depends on the size and shape of its crystals.

Here's why:

* Crystal size: Crystals form as magma or lava cools.

* Slow cooling: Allows for larger crystals to form.

* Rapid cooling: Results in smaller crystals or even a glassy texture.

* Crystal shape: The arrangement and intergrowth of crystals also affect texture.

* Equigranular: Crystals are roughly the same size.

* Porphyritic: Large crystals (phenocrysts) are embedded in a matrix of smaller crystals.

* Glassy: No crystals are visible, due to extremely rapid cooling.

So, the size and shape of the crystals within an igneous rock are the key factors that determine its overall texture.