骑行知识：三种岩石介绍

17.4公里，用时一小时零12分，比预想的快10分钟。

There are three main types of rocks in the world  igneous火成岩, sedimentary沉积岩 and metamorphic变质岩.

Igneous rocks火成岩 are formed from the cooling and solidification of molten magma or lava.  They can be classified as  Intrusive ( Formed inside the earth's curst地壳) or  Extusive ( Formed on the earth's surface).  Examples include  Granite basalt and  pumice花岗岩，玄武岩和浮石.

Sedimentary  Rocks沉积岩 are formed from  accumulation and cementation of Sediments over time, such as sand, clay, and organic material.  They can be further classified as  clastic碎屑构成的 ( Formed from fragments of other rocks), chemical ( Formed from the precipitation雨水 of minerals) and organic ( Found from the accumulation of organic material).  Examples include sandstone, limestone and shale砂岩石灰岩页岩.

Metamorphic rocks 变质岩are formed from the transformation of existing rocks due to heat, pressure or chemical reactions.  They can be classified as  foliated叶状( Having a layered or banded appearance) or non-foliated( Having a uniform appearance).  Examples include marble, slate and quartzite仓石板岩石英岩.

The origin of rocks can vary depending on the type.  Igneous rocks are formed from  Volcanic activity or the cooling of Magma deep within the earth's crust.  Sedimentary rocks are formed from the accumulation of sediment in bodies of water or on land.  Metamorphic rocks are formed from the transformation of existing rocks due to heat, pressure or chemical reactions.