Open Fracture — Surface-Reaching Cracks in Gemstones
Open Fracture — Surface-Reaching Cracks in Gemstones
Unhealed cracks that reach the surface of the stone, compromising durability and clarity
An open fracture is an unhealed crack or fissure in a gemstone that reaches the surface of the stone, in contrast to a healed fracture (where mineralisation has filled the crack and rebonded the structure) or an internal fracture (which does not reach the surface and is enclosed within the body of the stone). Open fractures compromise durability, provide pathways for dirt, oils, and water to enter the stone, and may propagate under stress, ultrasonic cleaning, or thermal shock. They are clarity features routinely noted in laboratory reports and they can affect value substantially, particularly where the fracture compromises a stone's appearance or its prospects for safe wear.
Identification
Open fractures appear under magnification as fine surface-reaching lines, typically following a crystallographic plane (in stones with cleavage) or a stress direction (in stones with conchoidal fracture). They are most easily detected by tilting the stone under directional illumination so that light reflects from the fracture plane, producing a flash that distinguishes the open fracture from internal features. A loupe at 10x magnification is sufficient for most open-fracture detection; more subtle features may require microscope examination.
The distinction between open and healed fractures is a matter of laboratory observation. A healed fracture appears as a series of sub-surface inclusion patterns — typically the 'fingerprint' inclusions of natural sapphire, ruby, and other species where post-formation mineralisation has filled and rebonded the crack. An open fracture, by contrast, shows a clear surface-reaching line and may exhibit characteristic light reflection from the fracture face.
Implications for durability
Open fractures are the principal durability concern in clarity grading. The crack provides a path for stress concentration, and any blow or thermal shock can propagate the fracture through the body of the stone. Open fractures parallel to a cleavage direction are particularly dangerous: a fracture aligned with cleavage in topaz, kunzite, or fluorite can propagate readily and split the stone.
Open fractures also create maintenance and care concerns. Dirt and oils accumulate in the surface-reaching crack and can be difficult to remove without ultrasonic cleaning, which itself may propagate the fracture. The combination of accumulation and cleaning risk creates a maintenance dilemma that frequently results in a slow degradation of the stone's appearance over time.
Open fractures in emerald and the resin-fill question
Emerald is the species most often encountered with significant open fractures, and the entire emerald trade has developed around the management of this clarity issue. The vast majority of commercial emeralds have surface-reaching fractures, often referred to in the trade as 'jardin' (French for garden), reflecting the network of fissures characteristic of the species. The standard treatment is impregnation with cedarwood oil or a polymer resin (such as Opticon) to reduce the visibility of the fractures by matching their refractive index to that of the host emerald.
Disclosure of fracture filling is mandatory in the emerald trade, with grades from minor to moderate to significant filling reflecting the quantity of resin or oil present. Buyers selecting emeralds should expect some level of fracture and filling and should select stones where the filling is at the lower end and where the fractures themselves are well distributed rather than concentrated in a way that compromises durability.
Open fractures in other species
Sapphire and ruby occasionally show open fractures, although the species' high hardness (Mohs 9) makes them less common than in emerald. When present, open fractures in corundum may be associated with heat treatment — the heating process can sometimes propagate pre-existing healed fractures and open them.
Aquamarine, topaz, kunzite, and tanzanite all show open fractures with some frequency, particularly along cleavage directions. These species require careful inspection before purchase and conservative wear (avoiding ultrasonic cleaning, thermal shock, and impact) to prevent propagation.
In the trade
Laboratory reports describe open fractures explicitly, distinguishing them from healed fractures and from internal inclusions, and indicating their location and size. GIA clarity grading treats open fractures more seriously than internal features of equivalent size, reflecting the durability concern. Buyers selecting stones for daily-wear ring use should pay particular attention to open fractures and either avoid stones with significant surface-reaching fractures or accept the durability constraints involved. See also healed fracture, fracture filling, and clarity grading for related entries.