A turntable stylus is there to be reproduce sound by ‘reading’ the grooves of a record. In order to that properly stylus’ are made from steel or even diamond. Why are these materials used?
The basic function of the stylus
In order to understand why a stylus id made from such hard material, we need to understand the function of the stylus and also the physics of both sound and matter.
How does a stylus work
The turntable stylus or needle is to placed in the grooves of the record. By than spinning the record the stylus will start to vibrate. This vibration is caused by the shape of the grooves, the edges of the groove are not flat and even the dept can variate. Because of these variations in the groove, the stylus will ‘bounce through the groove in stead of just slide through it. These bounces are the vibrations. The picture below explains how that process is working. You can see the needle/stylus of the turntable inside the record groove.
Note: This needle is completely filling the groove, thereby making contact with a large area at the same time. This means that very detailed or subtle information might be missed.
The problem of this needle that it is to big for the groove (or the groove to small). But by making the grooves bigger, the record could store less sound. So the solution is to make the stylus smaller so that the grooves as well can be made smaller.
1. Smaller needles means harder needles
In order to make the needle as small as possible, the needle needs to be thinner. And that is why the material needs to be so hard. When a material is hard, that means that the atoms are placed close to each other and very tight attached. You can therefore very precise cut away atoms without breaking the whole object. The tighter the atoms are packed together, the more precise you can be with shaping the object. In other words, the harder the material the smaller or sharper you can make the edges or point. This is also the case for a record player stylus. When the hardest material is used, the grooves can be made much smaller and thus more music can be put on that record. The second benefit is that the needle will be made more sensitive, when the point is smaller the stylus will be able to pick up more subtle variations from the groove. And thus produce a higher sound quality.
2. Wearing out the record or stylus
The second reason for the material for the stylus is the wear of the materials. Both the record as the needle can wear each other. Because of the contact with the record, the stylus will wear as is shown below. 
- A Stylus is new
- B After 1 record
- C After 10 records
This is an old steel stylus that is completely destroyed by the record. Because of one small stylus (<1 mm) is getting in contact with a very long groove (600+ yards). Because of the difference in surface, the needle will wear much faster. Thereby making the need for a more solid material. In summary ther are two reason for the solid materials used for a record player stylus: 1. A harder stylus does mean more and better sound 2. A harder stylus does mean longer duration of the stylus
