Baiduri

Baiduri; بايدوري (اوڤل)
	; A rich seam of iridescent opal encased in matrix
Maklumat am
Kategori	Mineraloid
Formula kimia	Silika terhidrat. SiO2·nH2O
Pengecaman
Warna	Colorless, white, yellow, red, orange, green, brown, black, blue, pink
Tabii hablur	Berira tidak tentu secara gugus atau nodul
Sistem hablur	Amorf
Pembelahan	Tiada
Fraktur	Conchoidal to uneven
Kekerasan skala Mohs	5.5–6
Kilau	Subvitreous to waxy
Kilau gilapan	Vitreous to resinous
Indeks biasan	1.450+0.020; −0.080; Mexican opal may read as low as 1.37, but typically reads 1.42–1.43
Sifat-sifat optik	Single refractive, often anomalous double refractive due to strain
Dwibiasan	Tiada
Pleokroisme	Tiada
Pendarfluor ultraunggu	black or white body color: inert to white to moderate light blue, green, or yellow in long and short wave, may also phosphoresce, common opal: inert to strong green or yellowish green in long and short wave, may phosphoresce; fire opal: inert to moderate greenish brown in long and short wave, may phosphoresce
Spektrum penyerapan	green stones: 660 nm, 470 nm cutoff
Guris	Putih
Graviti tentu	2.15+0.08; −0.90
Ketumpatan	2.09
Ciri-ciri diagnostik	Menggelap sebaik dipanaskan
Keterlarutan	air garam panas, bases, metanol, asid-asid humik dan hidrofluorik
Diafaneiti	legap, lutcahaya, lutsinar

Baiduri (Jawi: ‏بايدوري‎code: ms is deprecated ‎) atau opal ialah bentuk silika amorf yang terhidrasi (SiO₂·nH₂O); kandungan airnya boleh berkisar antara 3 hingga 21% mengikut berat, tetapi biasanya antara 6 dan 10%. Kerana watak amorfnya, ia diklasifikasikan sebagai mineraloid, tidak seperti bentuk silika yang kristal, yang dikategorikan sebagai mineral. Ia didepositkan pada suhu yang agak rendah dan boleh berlaku di fissures hampir semua jenis batu, yang paling biasa didapati dengan limonit, batu pasir, riolit, marl, dan basal. Opal ialah batu permata negara Australia.^[2]

Batu ini mempunyai dua kelas yang luas: baiduri berharga yang dibezakan melalui ketampakan berbilang warna berbanding baiduri biasa.^[3] Pemerhatian ini dapat ditakrifkan sebagai "kesan optik pseudokromatik yang menghasilkan kilauan cahaya berwarna daripada mineral tertentu, kerana ia berubah menjadi cahaya putih." ^[4] Struktur dalaman opal berharga menyebabkan ia menguraikan sinaran cahaya, menyebabkan mainan warna. Bergantung kepada keadaan di mana ia terbentuk, opal mungkin telus, lut atau legap dan warna latar belakang mungkin putih, hitam atau hampir apa-apa warna spektrum visual. Opal hitam dianggap paling jarang, manakala putih, kelabu dan hijau adalah yang paling biasa.

Hubungan dengan manusia[sunting | sunting sumber]

Batu ini merupakan antara barangan permata yang saling didagangkan antara para pedagang tanah India yang ingin mendapatkan hasil hutan seperti kayu jati, rempah ratus, getah damar dan haiwan eksotik^[5]^:92-94 dengan warga setempat kepulauan Nusantara sehingga tercermin pada asal nama "baiduri" yang meminjam dari Sanskrit: वैडूर्यcode: sa is deprecated vaiḍūrya.^[5]^:280

Batu ini amat didambakan di dunia Barat kerana kelangkaan ia yang sukar didapati melainkan di Červenica, sebuah kampung di pedalaman Slovakia,^[6] sehingga abad ke-19. Oleh itu, ia merupakan barangan bernilai tinggi direbut milik dalam kalangan raja-ratu kerajaan-kerajaan Eropah.^[7]^[8]

Rujukan[sunting | sunting sumber]

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
^ "Australian National Gemstone". Australian Government, Department of the Prime Minister and Cabinet. Dicapai pada 10 June 2018.
^ "Opal Description". Gemological Institute of America. Dicapai pada 4 June 2018.
^ "Glossary: Play of Color". Mindat. Dicapai pada 4 June 2018.
^ ^a ^b Hoogervorst, Tom (2012). Southeast Asia in the ancient Indian Ocean World: Combining historical linguistic and archaeological approaches (Tesis). Oxford University.
^ Finlay, Victoria. Jewels: A Secret History (Kindle Location 1871). Random House Publishing Group. Kindle Edition.
^ "The central stone on the thirteenth-century crown of the Holy Roman Emperor was an opal said to be the color of pure white snow, sparkling with splashes of bright red wine: it was called “the Orphanus,” perhaps because there was no other stone like it.24 And on New Year’s Day 1584,25 Queen Elizabeth I was delighted to receive an opal parure—a full set of matching jewelry—from one of her favorite courtiers, Sir Christopher Hatton." Finlay, Victoria. Jewels: A Secret History (Kindle Locations 2145-2148). Random House Publishing Group. Kindle Edition.
^ Finlay, Victoria (2005). Jewels: A Secret History (ed. elektronik Kindle). Random House Publishing Group. m/s. 2163–2165. All of these early stones were almost certainly from the ancient mines of Slovakia—the same source as Nonius’ precious stone and the Holy Roman Emperor’s red-and-white one. The mines were worked until the late nineteenth century...

Bacaan lanjut[sunting | sunting sumber]

Eckert, Alan (1997). The World of Opals. Wiley. ISBN 9780471133971. OCLC 36352362.

Pautan luar[sunting | sunting sumber]

Farlang opal Hist. References Localities, anecdotes by Theophrastus, Isaac Newton, Georg Agricola etc.
ICA's Opal Page: International Colored Stone Association
Opal Fossils from the South Australian Museum Diarkibkan 2014-02-13 di Wayback Machine Accessed 19 October 2016.

[GRG-1] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6

[2] "Australian National Gemstone". Australian Government, Department of the Prime Minister and Cabinet. Dicapai pada 10 June 2018.

[3] "Opal Description". Gemological Institute of America. Dicapai pada 4 June 2018.

[4] "Glossary: Play of Color". Mindat. Dicapai pada 4 June 2018.

[Hoogervorst-5] Hoogervorst, Tom (2012). Southeast Asia in the ancient Indian Ocean World: Combining historical linguistic and archaeological approaches (Tesis). Oxford University.

[6] Finlay, Victoria. Jewels: A Secret History (Kindle Location 1871). Random House Publishing Group. Kindle Edition.

[7] "The central stone on the thirteenth-century crown of the Holy Roman Emperor was an opal said to be the color of pure white snow, sparkling with splashes of bright red wine: it was called “the Orphanus,” perhaps because there was no other stone like it.24 And on New Year’s Day 1584,25 Queen Elizabeth I was delighted to receive an opal parure—a full set of matching jewelry—from one of her favorite courtiers, Sir Christopher Hatton." Finlay, Victoria. Jewels: A Secret History (Kindle Locations 2145-2148). Random House Publishing Group. Kindle Edition.

[8] Finlay, Victoria (2005). Jewels: A Secret History (ed. elektronik Kindle). Random House Publishing Group. m/s. 2163–2165. All of these early stones were almost certainly from the ancient mines of Slovakia—the same source as Nonius’ precious stone and the Holy Roman Emperor’s red-and-white one. The mines were worked until the late nineteenth century...

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