The Australian Open is played on hard courts, despite clay courts offering players more endurance. Here's why.

• The French Open is the only one of the four grand slam tournaments on clay courts.

• Despite their name, clay courts aren't made of clay. Instead they have a solid base like limestone and a fine layer of crushed brick.

• Clay courts give a slow ball speed, provide a medium to high bounce, and, because of the layer of crushed brick, the ability to slide.

• Visit Business Insider Australia’s homepage for more stories.

The Australian Open is played on hard courts, but why isn't it be using clay courts?

According to Tennis Australia, there are four main categories of tennis court surfaces, including clay (or pourous), natural grass, hard court and others such as carpet or floorboard.

In terms of Grand Slams, Wimbledon is played on a grass court, the French Open on clay, and both the US and Australian Open on hard courts.

But why isn't the Australian Open played on clay courts?

There are different varieties of clay courts including the traditional red courts, mainly in Latin America and Europe, green clay courts in the US called Har-Tru, Ant Bed in Queensland and "En Tout Cas" in Victoria.

Despite their name, clay courts aren't made of clay, because it absorbs too much moisture. Instead, most of the red clay courts are made of a solid permanent base like limestone, with a fine coat of crushed brick on top.

According to The Conversation, clay courts are the slowest court surface because of the amount of friction created by the ball when it hits the dirt.

The benefits of clay courts

Tennis player Rafael Nadal, who was recently knocked out of the Australian Open, is informally known as the 'King of Clay' as he has won the French Open 12 times.

While clay courts give a slow ball speed, they provide a medium to high bounce, a top spin and, because of the layer of crushed brick, the ability to slide. They are also beneficial for training as they have a softer surface and can improve endurance.

Dr James Zois, Lecturer in Sport Coaching at Victoria University, told Business Insider Australia in an email that the advantages of clay courts are more from a player development perspective.

"The ball travels slower and bounces higher on clay which means points last longer," he said. "This creates an opportunity to hone in on skills pertaining to ball placement, point strategy, patience during points, and longer rallies. [It] also helps to create more powerful athletes because the player is forced to generate more of their 'own pace on the ball'; instead of using speed generated from the surface of the court."

Clay courts also lead to longer rallies.

"The longer rallies/matches consequently can produce athletes with higher endurance capacities as their playing time is greater," Zois added.

Disadvantages of clay courts

Because of longer rallies, clay courts can also ramp up the likelihood of an injury.

"It can increase the chance of repetitive strain injuries due to the longer rallies and time on court," Zois said via email.

"Also, most major tournaments are played on much faster surfaces, so there are some adjustments that traditional clay-court players need to make in order to be competitive on the faster surfaces."

Another issue with clay courts is maintenance. While all court surfaces need maintenance, clay generally requires more care as they need to be cleared of plant debris and watered. Tennis Australia said. A well-maintained clay court, however can last for 10 to 20 years or longer.

Australia's effort to ramp up the use of clay courts

Because clay is used on more international tournaments than any other surface, Tennis Australia believes more up and coming players should train on it.

In 2010, Tennis Australia announced a $1 million initiative to build eight new clay courts in Melbourne Park, where the Australian Open is played.

At the time, Tennis Australia's then-President Steve Healy said Australia's "harsh climate, short supply of water, high cost and labour intensive nature of maintenance" has made it hard to "develop enough international quality clay courts and sustain them."

Zois also believes Aussies should be encouraged to play on clay courts.

"This is the best way to learn the tactics of tennis whilst giving the young athletes time during points to develop correct footwork, balance and coordination," he said via email. "In saying that, we have four different surfaces that the Grand Slams are played on, so practicing on all four of these surfaces is ideal."