Linga worship (Estate of Cynthia and Harlen Welsh
Lingam or Linga is the Sanskrit word for mark. Linga is also the word for gender, as in pursha-linga, sexual organs, and penis.
It is used as a symbol for the worship of the Hindu God Shiva. A stone lingam is a naturally occurring ovular stone, also associated with Hinduism. The term is not used in the Vedas but used frequently in the Mahabharata.
The linga (sign) is a symbol of Shiva. The linga is a phallic symbol, and represents the fertility of Nature.
Many Hindus consider it to be liturgically incorrect to worship images of Shiva himself, thus they substitute the lingam stone.
Satguru Sivaya Subramuniyaswami explains in the lexicon section of his book, Dancing with Siva, that "Sivalinga is the most prevalent icon of Siva, found in virtually all Siva temples. It is a rounded, elliptical, aniconic image, usually set on a circular base, or pitha. The Sivalinga is the simplest and most ancient symbol of Siva, especially of Parasiva, God beyond all forms and qualities. The pitha represents Parashakti, the manifesting power of God. Lingas are usually of stone (either carved or naturally existing, svayambhu, such as shaped by a swift-flowing river), but may also be of metal, precious gems, crystal, wood, earth or transitory materials such as ice. According to the Karana Agama, a transitory Sivalinga may be made of 12 different materials: sand, rice, cooked food, river clay, cow dung, butter, rudraksha seeds, ashes, sandalwood, dharba grass, a flower garland or molasses."
As Shri K. Thirugna Sambantha, in his excellent web site of Saivism,  (http://www.geocities.com/shivaperuman/main.html), explains it, the Siva linga is the ruparupa aspect because it is not any manifested form of Siva, nor is it formless, because the linga is a concrete piece of stone... it is [an] intermediate between the formless Absolute, Parasiva, which is beyond the sensory perception of man and manifest forms of Siva.
In popular culture
Something that resembled a Siva linga was called the Sankara Stone in the movie, Indiana Jones and the Temple of Doom.
- Schumacher, Stephan and Woerner, Gert The encyclopedia of Eastern Philosophy and religion, Buddhism, Taoism, Zen, Hinduism Shambala, Boston, (1994) ISBN 0-87773-980-3
Swami Sivananda's explanation about Linga being a Symbol of Shiva:
- The Siva-Linga: A Symbol Which Points To An Inference. (http://www.dlshq.org/download/hinduismbk.htm#_VPID_110)
- Linga, symbol of Shiva, God who is formless, attributeless and omnipresent. (http://www.shaivam.org/shplinga.htm)
-  (http://www.exoticindiaart.com/article/shivalinga)Shiva Linga