Mutton fat jade

Mutton fat jade is the top grade of white nephrite: a warm, slightly creamy white with a greasy luster and a very fine, even texture, likened to sheep fat that has cooled and set. Its Chinese name is yangzhi yu (羊脂玉), “sheep-fat jade”. It is a quality grade, not a separate mineral or variety, and there is no agreed line for where it begins.

What mutton fat jade is

It is nephrite, one of the two true jades, and not jadeite. White nephrite is the magnesium-rich, low-iron end of the tremolite-actinolite mineral series, which is why it is white and not green. A Gems & Gemology study of white nephrite, published by GIA, describes the best nephrite from Xinjiang as white with a greasy luster and says this is what the trade calls mutton fat jade.

The longer Chinese name is yangzhi baiyu (羊脂白玉), “sheep-fat white jade”. The comparison is to rendered fat just after it has set: white, soft-looking and glossy.

In the Chinese trade the word is used for nephrite in which three things reach the top level at once: fineness of texture, oiliness and color. For the mineral itself, see nephrite jade.

What it looks like

Feature	What dealers look for	What counts against a stone
Color	A warm, soft white with a faint cream or yellowish tint, like milk or fat	A dead paper white; any gray or green cast
Luster	Greasy, not glassy	A glassy surface
Translucency	Nearly opaque in ordinary light, glowing only with a strong light behind it	A glassy, see-through look
Texture	Very fine and even, with no visible grain	Visible grain or structure
Flaws	Almost none	Cracks, spots, cloudy patches, brown “sugar” staining

Two of these surprise newcomers. Oiliness matters more than whiteness: the luster is what the name refers to, and to dealers a very white piece without it is ordinary white nephrite. And the dense, oily look goes with low translucency, so glassy, translucent white nephrite is graded lower. That is the reverse of how jadeite is judged.

The color side of the subject, including the other white stones sold as jade, is covered in white jade.

Where it comes from

The classic source is Hetian (Khotan) in Xinjiang, below the Kunlun Mountains of western China. Gem-A reports that Chinese production from this region is shrinking.

Nephrite reaches the market in two main forms. Mountain material (shanliao, 山料) is quarried from the primary deposit as angular blocks. Seed material (ziliao, 籽料) broke away long ago and was tumbled down rivers into rounded pebbles, often with an iron-stained skin. The most sought-after mutton fat pieces are river pebbles that keep part of that skin. A Gems & Gemology note from GIA describes mutton fat nephrite with a natural dark brown, brown or brown-yellow oxide skin as rare and high grade, the skin having formed by natural weathering while the pebble was polished by river currents. Raw jade explains how rough of both kinds looks and is sold.

Xinjiang is no longer the only source of fine white nephrite. The Gems & Gemology study notes that white nephrite from the Baikal region of Russia, Chuncheon in South Korea and Qinghai in China has similar characteristics and is difficult to distinguish with the unaided eye or even under a microscope, and that material from other places has been falsely sold as Xinjiang nephrite to fetch higher prices. Dealers confirm it: very good Russian and Korean white is regularly sold as Xinjiang mutton fat, and at the top grades nobody can reliably tell the origins apart by eye.

Why collectors prize it

White nephrite has been the Chinese ideal of jade for a very long time. Nephrite has been valued in East Asia since the Neolithic, and Gem-A lists the white mutton fat variety among the most prized nephrite. According to the Gems & Gemology study, white nephrite from Xinjiang has kept the highest price in the Chinese market. With production from the classic source shrinking, supply is short. How scarcity and demand shape jade prices in general is the subject of why jade is expensive.

There is no agreed line

Dealers have a line for it: a thousand people have a thousand mutton fats. One seller’s mutton fat is another’s merely good white jade. Experienced collectors tend to avoid the word altogether and describe what they see: how white, how fine, how oily.

Three consequences follow.

A label on a cheap piece means little. Dealers note that laboratories differ in how strictly they apply the term, and that material sold cheaply under the name is ordinary white nephrite at best.

A laboratory cannot settle the name. A lab can confirm that a white stone is nephrite and whether it has been dyed or filled. Whether it deserves to be called mutton fat is a judgment of quality.

The term gets stretched. Some sellers market very fine, oily black nephrite as “black mutton fat”. Others in the trade dismiss that as hype. It is a sales phrase, not an accepted category.

Five common mistakes

1. Whiter is better. The white should be warm, and whiteness without oiliness does not qualify.
2. Any white nephrite qualifies. The name is meant for the rare piece where color, fineness and luster are all at the top together.
3. It must be a river pebble. River origin is prized but is not part of the definition. Dealers point out that mountain material can also reach the top white grade, and that many river pebbles are greenish or flawed.
4. It must have skin. Skin adds value today. A few decades ago it was routinely cut away.
5. It must come from Xinjiang. Xinjiang is the classic source and commands the premium, but the grade describes the stone. Similar white nephrite from Russia, Korea and Qinghai is sold under the name and cannot be told apart by eye at the top grades, so an origin you cannot verify is a story, not a property of the stone.

Imitations

The premium on skinned pebbles has produced a steady supply of fakes.

• Manufactured pebbles. GIA reports that white nephrite artificially polished into pebble shapes and partly dyed brown-orange is often seen in China as an imitation of skinned mutton fat jade. Dealers describe quarried material from cheaper sources being tumbled, dyed and baked to pass as Hetian seed pebbles.
• Filled and colored cavities. GIA has documented nephrite bracelets whose cavities were filled and colored to mimic dark skin.
• Stones that are not nephrite. Marble, sold in China as “Afghan jade”, is often banded and is only about 3 on the Mohs scale. Quartzite is glassy and granular. Neither has nephrite’s greasy luster.

In the first two cases the stone may well be real nephrite. What is fake is the pebble shape, the skin or the origin, which is where the extra price comes from.

What a buyer outside China can realistically do

Judge the stone, not the story. Look for a warm white, a greasy luster, an even body with no visible grain, and freedom from cracks, spots and cloudy patches. Treat pebble shape, skin and origin as claims you cannot check by eye.

Then have the testable part tested. GIA’s reference properties for nephrite are a Mohs hardness of 6 to 6.5, a specific gravity of about 2.95 and a refractive index of 1.606 to 1.632, and a gemological laboratory can confirm that a stone is nephrite and whether it shows dye or filling. Home checks narrow things down, and a lab report settles it. The report will not tell you the piece is mutton fat. The home checks are set out in how to tell if jade is real.