Intrusive igneous rocks don't always have shiny appearances. While some intrusive rocks can appear shiny, this is not a defining characteristic of all intrusive rocks. Here's a breakdown:

Shiny Appearance:

* Crystals: Many intrusive rocks cool slowly underground, allowing large crystals to form. These crystals can reflect light, giving the rock a shiny or sparkly appearance. This is particularly true for rocks like granite, which often contains large, visible crystals of quartz and feldspar.

* Mineral Composition: The mineral composition of the rock can also influence its shine. Minerals like quartz, feldspar, and mica, commonly found in intrusive rocks, can have reflective surfaces.

Not Shiny Appearance:

* Fine-Grained Texture: Some intrusive rocks cool more quickly, resulting in smaller crystals. These rocks, like gabbro, might have a more subdued, matte appearance.

* Weathering: Over time, weathering can dull the surface of intrusive rocks, reducing their shine.

* Rock Type: Not all intrusive rocks are created equal. Some, like diorite, might have a more muted color and less reflective surface compared to granite.

It's important to note:

* The "shininess" of a rock is subjective and can vary depending on the lighting and angle of observation.

* The size, shape, and arrangement of crystals, as well as the overall mineral composition, play a significant role in a rock's appearance.

Therefore, while some intrusive rocks can appear shiny due to the presence of large crystals and reflective minerals, it's not a universal characteristic. The appearance of intrusive rocks can be quite diverse.