Gem-Stones and Their Distinctive Characters

In Short

G. F. Herbert Smith’s Gem-Stones and Their Distinctive Characters is a comprehensive reference guide to identifying and valuing precious stones using physical science. Moving from theoretical optics, optical instruments, and specific gravity tests to detailed mineralogical surveys, the book explains how light, crystal structure, and human ingenuity intersect in fine jewellery. It remains a classic because it systematically demystified gemology at a moment when synthetic manufacturing and sophisticated imitations made optical instruments indispensable to jewelers and collectors alike.

The Story

The book opens with a clear proposition: distinguishing precious stones requires moving past traditional, unscientific tests toward the exact measurement of physical constants. To build this foundation, the author systematically lays out the physics of light as it interacts with gem material. He explains how light reflects and refracts when entering different media, defining Snell’s law, critical angles, and total reflection. This leads into an examination of lustre, sheen, and special optical phenomena like the six-rayed asterism found in star-rubies and star-sapphires due to internal tube-like cavities.

From basic refraction, the text moves to double refraction, dichroism, and polarization. Smith demonstrates how instruments such as the refractometer and dichroscope reveal a stone's optical character, allowing testers to observe twin colors or measure refractive indices directly. He then introduces methods for measuring specific gravity—ranging from heavy liquids like methylene iodide to hydrostatic weighing—and details Mohs’s scale of hardness alongside structural cleavage.

With these scientific tools established, the text transitions to the practical art of the lapidary. Smith explains how brilliant, step, and cabochon cuts are chosen to maximize a stone's inherent light, color, or dispersion. He explores historical and modern advances in synthetic production, highlighting Auguste Verneuil's 1904 inverted blowpipe apparatus that allowed artificial rubies to match natural gems.

The final two-thirds of the work systematically surveys specific gem species, starting with the diamond. Smith outlines the diamond’s commercial valuation rules, color grading systems, and geological occurrence, noting how steam pressure and molten iron drive diamond pipes upward. He then surveys corundum (rubies and sapphires), beryls (emeralds and aquamarines), garnets, zircons, chrysoberyls, opals, felspars, diopside, kyanite, and organic gems like pearls. Each entry detail the mineral’s chemical composition, optical constants, geography, and commercial nuances, completing a journey from abstract physics to physical gemology.

How It Unfolds

The laws of light The author introduces the fundamental behavior of light at the surface of gemstones, explaining reflection, Snell’s laws of refraction, and dispersion. He establishes that understanding light is essential because the primary purpose of a cut stone is to appeal visually to the human eye.

Optical and physical testing The focus shifts to discriminative scientific methods, detailing how to measure refractive indices, observe dichroism with specialized instruments, and calculate specific gravity using heavy liquids or hydrostatic weighing. Mohs’s scale of hardness is introduced to categorize a stone's resistance to abrasion.

Lapidary art and synthesis The text explores how lapidaries cut stones to enhance their intrinsic color or brilliance, while explaining technical breakthroughs like Auguste Verneuil's inverted blowpipe. This section demonstrates how synthetic rubies are manufactured using precise feeds of alumina powder through high-temperature oxygen-hydrogen flames.

The premier precious stones Detailed surveys examine the diamond and corundum groups, explaining commercial grading systems, historical price rules, and geological origins in places like South Africa and India. Structural characteristics, such as Ruskin's famous "Edwardes" ruby crystal in the British Museum, illustrate crystal habits and growth markings.

Semiprecious minerals and organic gems The survey expands to cover beryls, garnets, zircons, chrysoberyls, opals, and pearls, cataloging their specific gravities, refractive indices, regional sources, and unique internal structures. The book closes by detailing organic origin gems, measuring systems like the pearl grain, and famous historical specimens.

The People

G. F. Herbert Smith The author and scientific guide who seeks to provide a concise yet complete account of gemstone physics. He wants to equip both jewellers and the general public with accurate testing methods so they can identify cut stones with certainty rather than relying on unreliable old tests like the file.

Auguste Verneuil The inventive scientist who advanced synthetic gemology by creating an inverted blowpipe apparatus in 1904. He sought to overcome the barriers that baffled early experimenters, successfully manufacturing synthetic rubies that rivaled nature's finest productions.

William Crookes The scientist who put forward the theory explaining how diamonds were brought to the earth's surface. He posited that high-pressure steam acted as the primary propellant driving molten iron and crystallized carbon upward through geological pipes.

Henry Philip Hope The famous banker and collector who once owned the largest known pearl. His historic 454-carat cylindrical pearl stands as a primary example of exceptional weight and unique orientation in organic gem collections.

In Its Own Voice

"So long as the only confusion lay between precious stones and paste imitations an ordinary file was the solitary piece of apparatus required by the jeweller, but now recourse must be had to more discriminative tests, such as the refractive index or the specific gravity, the determination of which calls for a little knowledge and skill."

Smith introduces his first-edition preface by explaining why changing trade conditions demand that jewellers abandon crude tests in favor of precise optical and physical measurements.

"A stone may, for instance, be almost colourless except for a single spot of blue; yet, if the stone be cut steeply and the spot be brought to the base, t..."

In detailing the lapidary's craft, Smith notes how clever cutting can distribute localized color throughout an entire faceted sapphire.

"The deep-green alexandrite, for instance, is far more dichroic than the lighter coloured varieties of chrysoberyl."

While explaining the practical application of the dichroscope, Smith highlights how stronger inherent body color heightens the visibility of double-refraction twin colors.

What It's Really About

Beneath its clear classifications and tables of physical constants, Gem-Stones and Their Distinctive Characters argues that beauty in nature is fundamentally rooted in mathematical and physical order. Smith shows that a stone's charm—its fire, depth of color, or play of light—is not an abstract mystery, but the direct result of molecular structure, refractive index, and light interaction. The book advocates for the necessity of scientific literacy in a modernizing marketplace. As human ingenuity learned to synthesize nature's gems and create convincing imitations, empirical measurement replaced casual visual judgment. Ultimately, the work asserts that understanding the natural laws behind a gem's creation enhances both its commercial valuation and its aesthetic appreciation.

Why Read It Today

This volume remains a delightful read for mineral enthusiasts, historians of science, modern gemologists, and antique jewelry collectors. Smith writes with exemplary clarity and precise British restraint, free from sensationalism or modern marketing fluff. Reading it feels like taking a private tour through the British Museum's natural history collection with an exceptionally knowledgeable early twentieth-century curator.

The reader should be prepared for dense physical explanations, detailed mathematical formulas, and thorough listings of specific gravity numbers and refractive indices. Some historical details—such as early twentieth-century diamond prices, regional source names, and outdated geological theories—reflect its era, yet these elements offer a fascinating window into the gem trade of the 1910s. The text balances technical rigor with quiet wonder at nature's geometry, leaving the reader with a permanent appreciation for the physical laws hidden inside a polished stone.

<Elicitations message="Would you like to explore another aspect of this text?"> <Elicitation label="Explain Verneuil's method" query="Can you explain how Auguste Verneuil's inverted blowpipe produced synthetic rubies based on the book?"/> <Elicitation label="List gem hardness scale" query="What is Mohs's scale of hardness as detailed in G. F. Herbert Smith's book?"/> <Elicitation label="Compare ruby and sapphire" query="How does the book distinguish between rubies and sapphires in terms of optics and cutting?"/> </Elicitations>