Pearl.  Muktaa in Hindi. 

It is one of the nine gems. Other eight gems are (1) Heeraa - Diamond; (2) Pannaa - Emerald, Marakat; (3) Laal - Ruby, Chunnee, (4) Moongaa - Coral; (5) Neelam - Sapphire, Indraneel, Neelmani; (6)  Vaidoorya Mani; (7) Pukharaaj - Yellow Sapphire, Pushp-raag - all are called Mani or Ratn.

There is a common belief among Taantrik that when rain comes in Swaati Nakshatra to Earth it produces pearl in pearl oysters. The mollusk is then said to open its mouth to receive the first raindrops. When the same raindrops fall into the mouth of a cobra, they produce venom. The same raindrops also produce camphor when fallen in the banana plant; produce go-lochan (go-rochan or calcium) when they fall in the horn of a cow, and Bans-lochan or Bans-muktaa (or bamboo pearl) when they fall inside a bamboo shoot. Bans-lochan is known as Calcium bamboana and is mostly used in Aayur Vedik medicines.

[I have never heard of a Motee (pearl) in a coconut, which is called coconut pearl. I saw once a photo of coconut pearl with Richard Shaw Brown of Malayasia in "Sacred Objects" Group published on June 24, 2010. It was amazing. It came out from the green coconut. He has a site for his  museum of such materials www.richardshawbrown.com]

Myanmar is famous for its ruby, sapphire, and jade, no legendary accounts have been written about Melo melo pearls. For centuries the habitat of Melo melo shells has been known to exist along the coastal waters of Myanmar. The Mergui Archipelago has a long stretch of coastal area with over 800 islands. This area also produces some of the finest silver-pink and golden pearls. At pearl island hatcheries, pearls are cultured from bi-valve mollusks, Pinctada maxima and Pinctada mertensii.

With its intense orange color, unique flame structure, spherical shape, chatoyancy, porcellaneous luster, and durability, all these features combine to make Melo pearl amongst the rarest gems in the world. Since Myanmar coastal areas offer an ideal environment for the habitat of Melo gastropods, more exposure and education is necessary to upgrade its market.

Deep orange Melo pearl is rare, and it needs protection from Artificial light and natural sunlight (undue exposure to) as its Orangeness will fade to very light and sometimes to whitish/milk orange. Do not display in showcase with light. But best to keep in dark safe and shown only on request.

(1) Chandra Mani (Natural Oyster Pearl) - They are of Persian Gulf origin.
(2) Naag Mani (Snake Head Pearl) - Originated from South-East Asia (Ular Kembang Seribu Snake). These pearls come from cobra's hood and are perfectly round, like fish pearls, and they radiate a natural effulgence. By repeated washing, a snake pearl becomes as lustrous as a polished sword blade. Anyone possessing such a naga-mani attains piety, rare good fortune, and eventually becomes illustrious as a leader of men, complete with a great collection of all precious gems.
(3) Varaah Mani (Boar Head Pearl) - Originated from South-East Asia (Example from King Wild Boar head). Boar pearls are colored like a boar's tusks and are found only in remote parts of the world. Such pearls are auspicious symbols of the Varaah - Boar Incarnation of Vishnu.
(4) Gaj Mani (Elephant Head Pearl) - Originated from South-East Asia
(5) Matsya Mani (Ancient Fish Head Pearl) - Originated from South-East Asia- found in prehistoric water cave. Fish pearls are perfectly round and symmetrical. They possess a yellowish hue like the scales of the Pathenam fish which often inhabit the mouths of deep sea whales.
(6) Venu Mani (Bamboo Stem Pearl) - Venu Motee. Originated from South-East Asia (Puter Giling Bamboo Stem). Also called Bans Lochan, Bans Muktaa. Bamboo pearls appear like hailstones in color, and are found only within bamboo that has grown in a region populated by religious people. If it is from a black bamboo, it may be of black color also.
(7) Vriksh Mani (Tree Trunk Pearl) - Originated from South-East Asia
(8) Megh Mani (Cloud Pearl) - Or Sky Pearl. Originated from South-East Asia. There is no known method to identifying them.
(9) Shankh Mani (Conch Shell Pearl) - Originated from Caribbean. It is called Lakshmee Pearl also. Garud Puraan says - "Pearls from conch shells are usually the size of a large Kon (the large and of a drum stick), and they possess a color similar to their host shell." But sometimes they are round also, but they are rare.
(10) Coconut Pearl - This pearl is obtained from the rare coconuts. It is found in ripe dry coconut, some say where the stem joins. The coconut has to be opened to get it if there is one inside. It is hard and bit heavy and can be kept forever. Keep in your temple or wear as jewelry is best. It is not for worship it, as it is a Motee.

There is one Aakaash Mani (Meteor Motee) also which is next to impossible to get.

Snake and other pearls and fossils are acquired mostly in the Indonesian-Malaysian areas. They are discovered in caves, jungles, sacred places, and construction sites where the natives dig and find fossilized remains of snakes, animals, plants, trees, etc that contain these pearls. Chemistry testing on some samples which we conducted with the head of the GIA Research Lab in Bangkok, showed them to be mostly silica, just like petrified wood. But they were not able to be proved scientifically because there is no existing standard.
[see more at  http://www.agt-gems.com/NavaMoti.html]

How Much Do You Know About Pearl?
Did you know that 'cultured' pearls (nucleated and non-nucleated or tissue nucleated cultured pearls) and imitation pearls can be distinguished from natural pearls by X-ray examination? Nucleated cultured pearls are often 'pre-formed' as they tend to follow the shape of the implanted shell bead nucleus. Once the pre-formed beads are inserted into the oyster, it secretes a few layers of nacre around the outside surface of the implant before it is removed after six months or more. When you X-ray a nucleated cultured 'so-called' pearl it will reveal a different structure to that of a natural pearl (solid center with no concentric growth rings, compared to a solid center with growth rings). Many nucleated cultured pearls used in the trade today are in fact mostly shell bead nuclei with very thin to thin nacreous coatings over them. A natural pearl however is solid nacre or 100% pearl.

Any well equipped internationally recognized gem testing laboratory is able to separate natural pearls from their counterparts viz, cultured pearls, non-nucleated cultured pearls and imitation 'pearls'. One should NEVER purchase a natural pearl without a bona-fide gemological X-ray certificate. Some reasons being that good quality natural pearls are real, valuable precious jewels (while cultured-pearls are not), and only NATURAL real pearls, in "single divine unit" emit auspicious Moon energy (cultured pearls are near-powerless) . Although a real pearl is made of "nacre" still nacre in not a pearl. There fore a thin coating of nacre is NOT considered a real pearl. Ruby is made of red corundum, yet a coating of red corundum on a brick does NOT make a ruby; a cultured pearl is also on the same principle.