Margie Rogerson, the former longtime girlfriend of Bob Dylan, isn’t a musician, but she is a rock star when it comes to precious gems. It all started during the Summer of Love, when she sold her microminis to Bally of Switzerland, launching her Goldberry label and a career in couture. For an encore, she kept the name but changed the business, turning Goldberry into a glittering jewel box of a shop in Presidio Heights—all white and Lucite—and herself into a respected jewelry designer, dealer, and gemstone connoisseur. Rogerson’s hand-fabricated creations have won her a glittering clientele that spans both coasts and includes such diverse personalities as Willie Brown, Chick Corea, Dianne Feinstein, and Erica Jong. She spends days poring over stones and exposing fakes. As rubies rise and blue topaz falls, Rogerson surveys the fast-changing market and tells us when to buy and when to pass. Goldberry: 3516 Sacramento St., S.F., 800-507-5505

Even though most of your clients are men buying diamond engagement and wedding rings, you are famous for natural colored stones. What’s the attraction? Colored stones are more artistic, more unique, more romantic. For me, it is really about the color. That perfect lipstick-red ruby. That sparkling, Lake Tahoe–blue sapphire.

But diamonds are still the classic choice for wedding and engagement rings. A lot of people feel safer with a white diamond, though that is changing. Eighty-five percent of my customers are men buying engagement and wedding rings, and they are divided 50-50 between diamonds and colored stones.

The industry has advised us to pay attention to the “Four Cs”: cut, clarity, color, and carat. Does this still hold? Yes, but a new category, “cut grade,” or “light performance,” is being called “the Fifth C.” That has to do with the sparkle of the diamond. Right now, the only certification available for cut grade applies to the round brilliant shape, so “Ideal Excellent” is the best.

What level of diamond is a sure bet? There are only two ways you can’t be cheated: Buy a “D” in terms of color—it is going to be white. In terms of clarity, you don’t have to get anything above a VS2, which means “very slightly included.” Higher clarity is an advantage only if you’re buying the diamond as an investment.

Is it true that diamonds are not really rare? There are stockpiles, and

they occur in nature everywhere and in every country. It is just that De Beers is controlling their release. They are the oldest monopoly, and no one has ever been able to break it.

What’s the most precious stone right now? Rubies. They’ve gone up in price 300 percent in the past year and a half. An unheated natural stone is now $30,000 for four to five carats.

Speaking of price—what do you think about gold going through the roof? I don’t like gold and don’t sell anything in gold. All my jewelry is in platinum, which doesn’t wear down, so it’s better for holding stones. It’s also 35 times rarer than gold. Platinum was $828 an ounce in December ’03. It’s now about $2,100 an ounce.

What about fakes? Tell me about the diffused stone scandal. Five years ago, I went to the Tucson Gem Show to buy colored stones. The first day, the place was filled with orange padparadscha, the rarest, most expensive sapphire. The next day, they were pulled. Turns out they’d undergone a diffusion process developed by Russian physicists to artificially change the stones’ color.

Is there a governing body to regulate fakes? In the U.S., the American Gem Trade Association is the auth­ority on colored stones. Its lab certifies colored stones, so you know the country of origin and authenticity. You can’t just join; there are strict guidelines. There are only 24 members in California.

Where are you likely to get cheated? Anywhere. Price is your tip-off. If a high-quality, three-to-four-carat blue sapphire stone is $3,000, it’s diffused. You can’t buy a real precious stone for that price.

You’re also up in arms about irradiated diamonds and blue topaz. Many colored diamonds—blue, green, and red—are irradiated and potentially radioactive. In addition to being a possible health hazard, they are also more brittle and prone to breakage. All the blue topaz, a semiprecious stone, is irradiated, and some national jewelry chains—but not all of them—have pulled it.

This reminds me of the glow-in-the-dark numerals on watches made during the 1950s. It’s the same thing. But this is harder to trace, and no one knows about it.

How did you get interested in jewelry? I started as a customer, going downtown to look at stones. Then I saw the Habsburg collection in Austria. That’s the best stuff; the height of cutting for colored stones is around 1850.