Here are some history and Feng Shui usage of an Ammonite which i got from a website - earthfengshui
Not only is Ammonite important in Western civilization, but in Eastern culture as well. In the Orient, they call Ammonite the 'Kirin Stone', because the color pattern of the stone is similar to the scales of the auspicious mythical beast called the Kirin. The beast had the body of a deer, with the face and scales of a dragon. This creature is meant to bring good fortune and luck to all who see it.
Particularly important are the many colors of Ammonite. The multiple layers of color inside the stone is what creates the sparkling radiance. By examining the stone, one will see the seeds of seven distinct colors: ruby crimson, fiery orange, amber yellow, emerald green, jade, azure, and mauve. Hence, it has been appropriately named the 'Seven Color Prosperity Stone' by some Feng Shui masters.
From a Feng Shui perspective (the art of harmonizing nature) each color of Ammonite represents a different meaning. For example, Crimson stimulates growth and energy; Orange generates creativity, and increased libido; Green improves wisdom, intellect, and promotes entreprenerialship; and Yellow improves wealth. It is believed that the best combination of color for the stone is red, green, and yellow, for it represents a balance and signifies growth and richness. Other Feng Shui effects of the stone include the reversing of negatives into positives, and the reduction of the body's toxicity. It also promotes the flow of Ch'i (life force) through the body, enhancing wellbeing. Not only does it bring balance to the person's body, but also to that person's surroundings as well, such as the home or office. When the stone is placed in the home, it promotes a happy family, and when it is placed in the office, it promotes good business dealings. In essence, anyone who finds or possesses one of the stones is entitled to wondrous prosperity and fortune.
Also wrapped in the Ammonite is a harmonious balance of nature's five elements of metal, wood, water, fire, and earth. Therefore, Ammonite possesses special Feng Shui ability, expanding forces, and power. To those who possess it, and when placed in the household, brings balance and harmony to the home. Because all five elements are represented and compatible in Ammonite, it preordains the stone's auspiciousness.
From a scientific perspective, Ammonite is the fossilized rainbow-colored remains of a nautilus-like creature that existed over 70 million years ago, thus making it the oldest gemstone we know of today. The Feng Shui masters believe that because it is such an old gemstone with an organic origin, it has absorbed the plasmic energy from the universe since the beginning of time. The universe's forces follow the Ammonite's spiral from the periphery toward the center. And this centrifugal energy will then be radiated back through the stone, generating invisible spiritual, spiraling, and perpetual movements, bringing its owners health, wealth, and enlightenment.