Most Total Time Spent in Space. Soviet cosmonaut Sergei Krikalev holds this record, with a little more than 803 days accrued over six spaceflights. That's more than two years and two months spent zipping around the Earth.
Natural citrines are rare. Most commercial citrine is heat-treated amethyst or smoky quartz. Because the color is now caused by finely distributed iron minerals (mostly hematite and goethite), heated amethyst is not a citrine in the strict sense.Quartz colored by inclusions of any kind is not called a citrine.atural citrines are rare. Most commercial citrine is heat-treated amethyst or smoky quartz. Because the color is now caused by finely distributed iron minerals (mostly hematite and goethite), heated amethyst is not a citrine in the strict sense. Quartz colored by inclusions of any kind is not called a citrine.
The rarest diamond in the world based on size is The Cullinan Diamond originally weighing in at 3106.75 carats. That gem was then cut in nine large chunks, 96 small ones and 9.5 carats of unpolished pieces and put into the various British Crown jewels. The Cullinan is white in color. Other rare diamonds include: Recent trends have led the industry toward fancy yellow, champagne, brown, pink and even a few red diamonds out there. The natural occurrence of these colours is rare, and some vendors treat stones so that they become these more rare colours.