Rocks, minerals, and the study of the Earth.
Test your knowledge with these top questions!
Pumice consists mainly of which natural material?
Rapid cooling leaves little time for atoms in pumice to arrange themselves into a regular crystal structure.
Which feature of obsidian can reveal the volcanic source of an ancient stone tool?
Chemical fingerprints can link obsidian tools to distant volcanoes, helping archaeologists trace ancient trade routes.
Fulgurites formed in loose sand often take which shape?
The hollow tubes trace the electrical path through the ground, preserving a record of where the current traveled.
Pumice stones smooth calluses mainly by doing what?
Calluses form when repeated friction or pressure causes skin to build up a thicker protective layer.
Why do gardeners add pumice to potting mixes?
The hard grains keep a potting mix from packing tightly, leaving space for air around roots.
What usually makes the outside of a sandy fulgurite rough?
The inner wall melts more fully, so a rough outer coating can surround a smoother glassy tube.
What natural event can melt sand into a fulgurite?
The name "fulgurite" comes from "fulgur", the Latin word for lightning.
Pumice first forms during which natural event?
Expanding gas bubbles leave holes in pumice as frothy lava cools and hardens.
Obsidian is most commonly which color?
Thin edges of black obsidian can let light through, showing that a dark rock is not always opaque.
The pale spots in snowflake obsidian are made of what?
The spots grow as some of the volcanic glass changes into cristobalite, a crystalline form of silica.
Porosity measures the fraction of a rock's volume occupied by pore spaces. Permeability describes how easily fluid can pass through the rock. Water needs connected openings large enough to flow readily, so a highly porous rock can still transmit water poorly.
British Geological Survey definitions; USGS on groundwater flow