It is the birthstone of October, and zodiacs Taurus and Libra can also wear it as per Western astrology. It is an excellent alternative for diamond. 

Weight:     Typically, the gemstone size should be approximately 1/10th of your body weight, that means 1 carat for every 10 kgs. Alternatively, it can be according to the strength required as per your horoscope or as advised by your astrologer.
Quality:    For the best astrological results, Australian Opals are considered best.
Metal:     Silver, platinum and white gold
Finger:     The left hand's index finger for women and right hand for men is our recommendation. 
Day:        Friday
Time:        Morning
Mantra:    Om Shukraye Namah or Om Shukracharya Namah
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Benefits                          
A benevolent gem, it brings prosperity to the wearer and enhances relationships and fertility. 

Intimacy: It encourages healthy relationships leading to fulfilling marriages and strong companionships. 
Comfort: It brings remarkable material comforts and luxuries. 
Behaviour: It makes one irresistible and magnetic such that draws others to you. 
Imagination: It blesses the wearer with creativity and a vivid imagination to scale new heights.
Health: Healthwise it helps curb urinary infections, kidney problems and hormone issues.

Australian Opals are hugely preferred, followed by Ethiopian Opals. Opals come in two types: fire Opal and normal Opal.  Normal Opal is whitish while Fire Opal reflects an array of rainbow colours when held in the light.Opals can come in many colors other than white, even in black sometimes with a varying degree of transparency. Beware of doublet or triplet opals sold in market . Doublet or triplet opals are one’s which are sticked toghther & thus are available at a very low price.