### substance:

Pumice
* also cools so fast that within a few hours it looks like glass.
* can form from any types of magma, including basalt, andesite, dacite, and rhyolite.
* comes in many shades from cream through to orange.
* consists mainly of glass materials rather than mineral crystals
  - of fragments of vesicular magma formed during explosions
* cools off very quickly and also is associated with gaseous eruptions.
* extrusive igneous rock that light yellowish gray.
* flow stratigraphic subunits, distal limits of youngest pyroclastic flows and lahars.
* form of volcanic glass that's filled with holes.
* forms from a frothy, silica-rich magma.
* gaseous froth, formed by the expansion of gas in lava.
* has a tendency to break down during use becoming finer as it is used
  - many air pockets in it which helps it float in water
  - such a low density it can often float on water
* highly vesicular variety of rhyolite.
* is an example of a pyroclast
  - coarse tephra, ash is fine-grained tephra
  - crushed from volcanic rock
  - derived from cooled lava and is used as polishing and grinding stones
  - foamy volcanic glass, so light that it floats on water
* is formed from lava that is full of gas
  - when the pressure on the magma is reduced as it rises to the surface
  - found in bath tubs
* is ground up and used today in soaps, abrasive cleansers, and also in polishes
  - just like obsidian except it is tiny shards of glass
  - one kind of rock formed by volcanic eruptions that are very explosive
  - rocks
  - so light that it actually floats on water
* is the ash from volcanoes
  - hardened residue of volcanic froth, or very liquid rock highly charged with gases
  - principal ingredient in tuff
  - seeds and skins of crushed and pressed grapes
  - thus very light weight
* is used chiefly as an abrasive and is included in many scouring preparations
  - commercially for cleaning and polishing wood, metal, and other surfaces
  - for polishing hard things
  - in heaps of things like toothpaste, cement, and cosmetic products
  - usually felsic
* lava rock that is hardened foam.
* light gray porous lava that is found around certain volcanic vents.
* light, porous volcanic rock that forms during explosive eruptions.
* light-colored vesicular igneous rock.
* rock composed of little more than the sides of tiny bubbles.
* very light colored, frothy volcanic rock that is formed from lava that is full of gas

### substance:

Pure substance
* Most pure substances are compounds.
* Most pure substances consist of chemical elements
  - different elements
  - single elements
* Most pure substances have chemical properties
* Some pure substances exist in states.
* are either elements or compounds, two or more elements combined in unique ways
  - inanimate objects
* boil at a particular temperature and pressure.
* can be either chemical compounds or elements.
* change state at a particular temperature.
* have a melting point
  - specific gravity and the usual standard of that gravity is water
  - clear properties such as being a solid, liquid or gas at a certain temperature
* include elements.
* is the origin of all else.

Pyrogen
* act in the brain to reset the body's thermostat to a higher temperature than normal.
* are substances.
* can come from external substances such as bacteria, viruses, or toxins.
* make their way to the hypothalamus, which is in charge of regulating body temperature.
* stimulate the hypothalamus to raise the body's internal temperature, resulting in a fever.

Pyrophoric material
* can ignite spontaneously with no external source of ignition.
* ignite spontaneously in air.