Lord Shiva is also worshipped in ling form. According to scriptures, Lord Shiva is the universal spirit and is shapeless and so he is worshipped in the ling form.
According to Hindu scriptures, worshipping shivling gets best results. Many people place shivling even at their homes. People worhip shivlings made of crystal, saffron, black stone or mercury.
But, while placing a shivling at your house makes sure you keep the jaladhara too. The jaladhara is an important part of the shivling. If anyone worships a shivling without jaladhar then it invites bad energies.
It is believed that shivling appeared on earth in fire form. Placing it on earth was not possible. All the Gods went to Parvati for help. With her power parvati produces a jaladhar. It is believed that the jaladhar is a representation of Parvati. Hence, separating jaladhar from the shivling is considered bad.