Apart from Parad Shiva Linga or Narmadeshwar Shiva Linga no other form of Shiva Lingam should be worshipped at home.

According to ancient Hindu texts, it is believed that apart from Parad Shiva Linga or Narmadeshwar Shiva Linga no other form of Shiva Lingam should be worshipped at home. The Parad Shivalingam, also called the Rasalingam plays a very important role in Lord Shiva’s worship. Tamil Siddhas consider mercury as Shivadhatu- Shiva’s metal. Mercury is said to represent the male (Shiva) form and Sulfur used for solidification process is considered as the female form (Shakti). The Parad Shiva Lingam contains no other metal except Mercury. It can be made to powder by crushing and as well can be turned in to the Pure Mercury form by heating to the very high temperature comply with the Parad Sanmhita. When mercury is stabilized, its waves solidify. This process causes effect on the mind. If one meditates beside a parad Shivalinga, the mind naturally gets concentrated. Therefore, a solidified form of mercury is of great significance because it is extremely helpful in concentrating the mind.

It's is said the very touch of this mercury a person gets the benefit of Shiv Puja done in all the three lokas. Although mercury classifies under metals, it is in semi liquid form. Therefore, a Shivling made of mercury is also known as Ras Shivling.
Parad Shiva lingam is complete with 8 Sanskaars (8 stages of Purification according to Parad Sanmhita) and removal of Saptakanchuki (100% pure, medicated and hygienic); the Siddha Parad (Mercury mouth closed with Aghor Vidhya) is formed to make Murthi-Badhha / Agnibadha (heat resistant) Shiva lingam. It is said that worshipping the Parad Shivlingam gives 24 Ras and 5 Tatva which frees the body from all diseases.

A number of vedic references point out to the holistic benefits of Parad Shivalinga. ‘Shivnirnaya ratnakara’ states that there’s no better Shiva-linga ever made than the one made out of mercury.

** People who slaughter cow, malign others, veerghati, Who influence abortion, who trouble their parents the sins of such people can also be washed away by only the sight of Parad Shivlingam ~ Shiva Maha Purana

** Lord Shiva says to Goddess Parvati that anyone who worships the Linga made out of solid mercury will face no death, disease or dearth. ~ Sarvadarshana Sangraha.

** A million times more fruitful is worshipping a Parad Shivalinga than worshipping a thousand Shivalingams. Just looking at a Parad Shivalingam neutralises the effect of sin of killing a thousand Brahmins and cows. The holiness, auspiciousness acquired by the sight and worship of purified Parad Shivlingam is crore times more then that of lakh of other Shivlinga. As just the sight of Parad Shivlingam neutralises an individual from dreadfull sins like thousands of Brahmahatya, Cow's laughter and on touching Parad Shivlinga person is completely relieved of all these sins as quoted by Lord Shiva himself. ~ Shiva Maha Purana

** Holy blessing which is obtain by performing 100 Ashwamegh Yagya, donating Lakhs of cows, donating ample of gold, and taking holy bath in all the four pilgrimage places (Char Dham) is equal to the sight (Darshan) of holy Parad Shivlingam. ~ Rasaarnnav Tantra.

** People who worship Parad Shivlinga with all the good virtues, attain the blessings of Shivlingam present in all the 3 Loka's (Swarga Lok) and also destroys all bad sins. Possession of Mercury Shivlingam, its touch, donation, meditation, worship washes away all the bad sins of present life and past life.

** A person who worships a Parad Shivalinga just once in his life surely gains Dharma (righteousness), Arth (wealth), Kaam (pleasures) and Moksh (spiritual progress).

** One enjoys all comforts in life and attains wealth, fame, position, respect, sons, grandsons, high education and prosperity if one worships a Parad Shivalingam just once in one’s life time. And such a person surely reaches a high position in life. ~ Brahmaveivart Purana

** Longevity, good health, prosperity and all desired achievements can be had through the worship of Parad Shivalingam ~ Vaayveeya Samhita

** The person who worships Parad Shivlingam at home is freed from all the sins and attains eternal happiness along with the blessings of Shivlingam present in all the three loka. ~ Swami Sacchidanand.
** Ravana was a Rassiddha Yogi, and hence he used to worship Parad Shivlingam through which he was able to make Lord Shiva happy, and through which he was able to make his kingdom of gold. Similarly Banasur (Rakshas) also worshipped Parad Shivlinga and attained his desired wishes. ~ Rudra Samhita

** Parad Shivlinga is Maha-Linga, also it is home to Lord Shiva's divine powers hence called "Shivalaya". It's attainment leads to prosperity and success. ~ Yoga Shikoupanishad Granth

** People of all the 4 categories according to Hindu Religion (Namely Brahmin, Kshatriya, Vaishya, Shudras) and even females can worship and attain blessings of Parad Shivlinga ~ Brahma Purana

Om Namah Shivaya