| GREISEN | Light-coloured rock containing quartz and mica formed from the alteration of granite by hot gases fr |
| SMOKE | Product of combustion consisting of fine particles of carbon carried by hot gases and air (5) |
| VOLCANO | A vent in the crust of Earth or another planet or satellite, from which issue eruptions of molten rock, hot rock fragments, and hot gases. Also: the subject of this puzzle. (7) |
| GNEISS | Pleasant-sounding rock composed of quartz and mica (6) |
| PYROCLASTICFLOW | A fluidized "flowing" mixture of hot rock fragments, hot gases, and entrapped air that moves at high speed in thick, gray-to-black, turbulent clouds that hug the ground. (11,4) |
| SANDSTONE | Rock containing quartz grains |
| SAND | Used to measure the passage of time in an hourglass, fine grains of quartz and other minerals forming a major constituent of coastal dunes, seashores, deserts and river beds (4) |
| GRANITE | IgneousA rock, generally composed of feldspar and mica and quartz (7) |
| HALO | Region of hot gases surrounding the Milky Way that is also known as the circumgalactic medium (4) |
| AMPHIBOLES | Minerals of a group of dark-coloured rock-forming silicates (10) |
| IDAHO | Containing within its rocks and stream beds some 72 different minerals including garnet, opal, topaz, rose quartz and amethyst, the US Gem State (5) |
| AMENDMENT | Meant somehow to conceal the repair and the alteration (9) |
| FIREBALL | Luminous sphere of hot gases at centre of nuclear explosion (8) |
| BIGBERTHA | Nickname of Lunar Sample 14321, a moon rock containing an Earth-origin meteorite collected by the Apollo 14 mission in 1971 (3,6) |
| BASALT | Dark-coloured rock produced by volcanoes (6) |
| SHALE | Rock often containing quartz |
| DIORITE | Rock composed of quartz and feldspar (7) |
| TOPAZ | It's between quartz and sapphire on the Mohs scale of hardness |
| FELSITE | A fine-grained volcanic rock mixture of quartz and orthoclase (7) |
| FLAKY | Like puff pastries and mica rock |
