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A word applied to two green minerals that look similar and have similar properties: jadeite (a kind of pyroxene ) and nephrite (a kind of amphibole ). Both minerals are formed during metamorphism and are found primarily near subduction zones, which explains why jade is abundant in a variety of locations along active plate boundaries.


A speckled or patterned silicate stone that appears in a wide range of colors. It is a variety of chalcedony.
Jasper forms when silica precipitates in a fine particulate material such as soft sediment or volcanic ash. The particulates give the stone its color and patterns.

jet stream

A fast-flowing, narrow air current found in the atmosphere. The polar jet stream is found at an altitude of 7 - 12 kilometers (23,000 - 39,000 feet), and the air within can travel as fast as 160 kph (100 mph). Jet streams are created by a combination of the Earth’s rotation and atmospheric heating.


A surface or plane of fracture within a rock.

joule (J)

The energy expended (or work done) to apply a force of one newton over a distance of one meter.


The geologic time period lasting from 201 to 145 million years ago. During the Jurassic, dinosaurs dominated the landscape and the first birds appeared.
The Jurassic is the middle period of the Mesozoic.