S: FDIR preface (last access: 12 October 2013)
N: 1. Igneous rocks (from the Greek word for fire) form from when hot, molten rock (magma) crystallizes and solidifies. The melt originates deep within the Earth near active plate boundaries or hot spots and then rises toward the surface. Igneous rocks are divided into two groups, intrusive or extrusive, depending upon where the molten rock solidifies.
2. Igneous rocks are produced by the crystallization and solidification of molten magma. Magma forms when rock is heated to high temperatures (between 625 and 1200° Celsius) beneath the Earth’s surface. The exact temperature needed to melt rock is controlled by several factors; chemistry of the rock material, pressure, presence of gases (like water vapor) all influence when melting occurs.
S: 1. V-Vulcan – http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Notes/igneous_rocks.html (last access: 12 October 2013). 2. EOE – http://www.eoearth.org/view/article/153764/ (last access: 20 October 2013).
SYN: fire rock
S: RH – http://www.fi.edu/fellows/fellow1/oct98/create/igneous.htm (last access: 12 October 2013)