At one time or another, we have all pressed our hands against a window and looked through a pane of glass to view the world outside (or the world inside the glass). most of us don’t give much thought to the amazing substance known as glass.

the type of glass used for windowpanes is translucent. translucent means that the glass is transparent, or clear. this allows people to see through the glass without any trouble. technical advances let people produce glass in many colors, shapes, and sizes for a variety of uses. however, mother nature creates glass without any outside .

natural glass forms in several different ways. whether formed naturally or through manufacturing, the most common way of making glass is to superheat silica or quartzite sand to its melting point. the sand along shorelines and beaches contains these two materials. after the crushed quartzite or silica is superheated into a liquid form, it cools to form a clear, hard substance. this is glass.

4scientists consider glass an amorphous substance. this means it is not truly a solid or a liquid. it exists in a state somewhere in between. though the molecules that make up glass have a messy arrangement, they still manage to bond together and become stiff. glass reaches this state once it has cooled after introduction to intense heat. in fact, the opposite is also true. introducing a piece of glass to extreme heat can return it to a liquid form.

5though this explains how glass forms, you might still be wondering how this takes place in nature. lightning is one way that glass can form in a natural setting. when a bolt of lightning hits a sandy patch of soil, it can create natural pieces of glass called fulgurites. this occurs in much the same way as we create glass synthetically. in this case, though, the bolt of lightning creates the extreme heat needed to form glass.

6glass also forms naturally when lava bursts from a volcano and then cools. the melting lava creates tremendous amounts of heat. it would then make sense that a natural byproduct of the fiery volcanic explosions is a glass formation called obsidian. obsidian is a beautiful, natural spectacle. known for its shiny black, orange, gray, or green color, it was surely the earliest type of glass used by prehistoric societies. it often forms when lava spews into the sea and the water cools the lava into hard volcanic glass. unlike translucent glass, obsidian is usually opaque. this means you cannot see through this type of glass.

it was through these natural events that people discovered the amazing substance known as glass. after its discovery, people began manufacturing glass and using it for many practical and artistic purposes. today, glass is an important part of our everyday lives. just look through any window!

8) according to the passage, which of these is true about the glass used for windowpanes?
a) it is opaque.
b) it is translucent.
c) it contains fulgurites.
d) it comes from volcanoes.

9) why did the author write this passage?
a) to people understand how lightning works
b) to explain how glass is formed in nature
c) to encourage people to make glass
d) to sell glass windows to readers

10) what is the main idea of this passage?
a) clear glass that you can see through is called "translucent."
b) obsidian is a type of opaque glass often formed around volcanoes.
c) glass also forms naturally when lava bursts from a volcano and then cools.
d) glass is an amazing substance that can be formed naturally or manufactured.

11) which section most clearly supports the generalization that everyone uses the amazing substance known as glass?
a) section three
b) section four
c) section five
d) section seven