Gypsum is an incredibly soft mineral and it can in no way scratch glass.
To help you understand why this is, let’s take a closer look at the properties of each material to see what makes them different.
Can Gypsum Scratch Glass? (EXPLAINED)
What is Gypsum?
Gypsum is the most common sulfate mineral, and it is most commonly found in sedimentary deposits along with other minerals such as sulfur, calcite, dolomite, anhydrite, and halite.
Formed as an evaporate mineral, it crystallizes as translucent selenite.
As a mineral, gypsum is not very durable, and only reaches a 2.0 on the Mohs hardness scale.
It is also moderately water-soluble, although it becomes less soluble at high temperatures.
When heat is applied in air, gypsum can actually lose water and convert to calcium sulfate hemihydrate.
If continually heated, it can convert to anhydrite.
Because it has such low durability, it isn’t often used for ornamental purposes, but rather in the manufacturing of cement, plaster of Paris, and wallboard.
That said, in certain conditions, such as those found in the Naica Mine in Chihuahua, Mexico, gypsum can thrive and grow to be quite large.
In this particular location, crystals have even been found measuring up to 36 ft long, making them a striking sight to witness.
See also: Is Gypsum a Metal?
What is Glass?
Glass is all around us and everyone is familiar with it to some extent.
However, beyond being used in windows, cars, and smartphones, most people don’t think about what exactly this material is.
The glass that we are most familiar with is silicate glass, a manufactured variety that is based on the compound silica, which is the primary component of sand.
Soda-lime glass constitutes around 90% of manufactured glass and contains about 70% silica.
Although the term glass is most commonly used to refer to this material, silica-free glass is another variety with desirable properties when it comes to communication technology.
Despite being relatively brittle, silicate glass can last for long periods and there are surviving examples from at least 3,600 BC, in Mesopotamia, Syria, and Egypt.
While most people are familiar with these manufactured examples of glass, naturally occurring glass can be found throughout nature.
Caused by several different geological processes which involve melting and rapidly cooling rock, the most common examples are those produced by magma that makes its way to the earth’s surface.
Obsidian is the most well-known type of glass that is created by volcanic activity.
The hardness of glass can vary between 4.0 to 7.0 on the Mohs scale, meaning that anything higher on the scale can scratch it and anything lower cannot.
Glass plates are often used for scratch tests to determine the hardness of an unknown mineral, but they are far from the other tools which we will explain further down.
Can Gypsum Scratch Glass?
When it comes to determining whether or not gypsum can scratch glass, we need only look at their places on the Mohs hardness scale.
For example, if we have a sample of glass that ranks 5.0 on the scale, it’s evident that gypsum, which only has a hardness of 2.0, isn’t going to be able to scratch it.
However, glass, being harder, is capable of scratching gypsum.
Testing Hardness at Home
If you’re interested in testing hardness for yourself, there are numerous ways to do this.
For instance, you could use a glass plate as a testing medium to see whether or not a specimen is harder or softer by scratching it along the surface.
However, there are also other testing tools that you can make use of to help gauge the hardness of an object.
For example, when testing gypsum, you can use your fingernail, which has a hardness of about 2.0 to 2.5.
Because it has the same hardness as gypsum, it will produce a scratch.
Quartz is one of the harder minerals that you can use for testing, with a hardness of 7.0, meaning it will scratch anything — including glass — that is softer than it.
Additionally, you can also use a streak plate, which has a typical hardness of 6.5 to 7.0.
Keep in mind that when using a streak plate, that a line left behind isn’t necessarily a scratch.
Gypsum, for instance, has a white streak that it can leave behind which is easy to wipe away.
It won’t actually etch a groove into the surface.
If you’re ever unsure, you can test for a scratch by feeling with your fingertip or using a hand lens to see if anything was left behind.
One alternative that you can also consider is using hardness picks, which have sharp metal tips which can be used for more accurate testing.
These picks give you more control, and will easily produce a scratch if they are harder than the material they are used on.
Sold in sets, each pick will have a point made from a material of different hardness, such as plastic, copper, and specially selected alloys.
The upside of these testing picks is that they are reusable and can be sharpened if they begin to dull.
Although they can be relatively expensive, the longevity and reusability of them can make them a great addition to a collection if you are serious about collecting and testing your own stones and minerals.
While gypsum won’t scratch glass, it does give a good example of how hardness factors into testing the hardness of stones and minerals.
If you’re interested in testing this for yourself, you easily can with any specimen and a piece of glass.