Yellow was the color of Chinese emperors, hence yellow Tianhuang gemstones were considered the "king of stones," the best of the best and symbol of royalty. The purer the yellow, the better.

It was said to bring longevity, fortune and health, like all good-luck stones.

Tianhuang (literally yellow stone from a field) was used for carving, especially to make seals.

It is a type of Shoushan stone, only found in Shoushan, Fujian Province, known as larderite by gemologists.

In ancient times, it was more highly prized than gold. There was a saying that "one liang of Tianhuang equals three liang of gold." A liang is a Chinese unit equivalent to 50 grams.

Today, good carved Tianhuang is worth far more than gold. The price has reached more than 10,000 yuan (US$1,500) per gram on the antique market.

In addition to yellow, some stone is marbled yellow and amber, some is white, red, black and other colors.

Tianhuang is found in the shape of eggs. It is said to have six main characteristics: xi (gentle), jie (pure), wen (mild), run (polished), ni (oily) and ning (crystalline).

"Tianhuang stone is the best seal stone and first among China's 'three precious seal stones'," says seal-carving expert Yuan Huiming. The other two are Jixue (bloodstone) and Furong (rose quartz) stones.

During the Ming (1368-1644) and Qing (1644-1911) dynasties, most Tianhuang stones were presented to the imperial palace as tribute. They were carved into seals and auspicious shapes and played a part in sacrificial offerings in the imperial palace in the Qing Dynasty.

Tianhuang was considered the "dream gemstone" of collectors and was sought by the literati and wealthy people as signs of high social position and taste.

Many lucky meanings are ascribed to the stone. The character fu, from Fujian where the stone was mined, means fortune. The character shou from the location Shoushan means longevity. And yellow is the imperial color.

In mythology, Tianhuang is the stone left behind by Goddess Nuwa when she patches up the sky. Another tale says Tianhuang is the transformed egg of the phoenix.

In appraising a stone, one must first determine whether it's real Tianhuang, says Li Yuanmao, an expert and collector who has written extensively on the stone. "There are many fakes on the market."

To tell a fake from a real, Li offers some tips:

Tianhuang stone is usually brownish yellow or brownish crimson and has more or less red lines or texture. Fake is often transparent.

Real Tianhuang stone usually has a very thin "skin" that is different in color from the inner part, while fake ones don't have such "outwear" and are often smooth on surface.

(Shanghai Daily January 12, 2009)