1.   Basalts are examples of basic volcanic rocks, while andesites are intermediate between basic and acid.

2.   Fresh volcanic rocks are poor conductors of electricity.

3.   Most volcanic rocks contain some phenocrysts - they are a bit like the pips in raspberry jam.

4.   RioFinex examined the Ordovician volcanic rocks of County Tyrone for base metals but found only minor intersections of low-grade copper mineralisation.

5.   The codename was chosen because rhyolite is a volcanic rock containing colourful pieces of quartz set in a mass of crystals.

6.   The fossils are sandwiched between two layers of volcanic rock.

7.   The important properties of these three principal volcanic rock groups can be summarized in simple tables.

8.   These are frequently associated with volcanic rocks of oceanic type.

9.   Thus the volcanic rocks formed are drastically different from their oceanic counterparts.