FS soil and glass

Describes the behavior of a substance without having to change composition of the substance
density, particle size (soil), refractive index (glass)

Velocity of light in vacuum/velocity of light in medium
Intensive physical property (amount doesn't matter)
Light in air: 300 million meters/sec
The higher the refractive index, the slower the light travels through the medium

Bending of light as it moves from one medium to another

Known or consistent chemical composition- rocks and minerals
Repeating geometry shape
Quartz: lattice structure (macroscopic)

Atoms are random and disorderly (glass, cannot use chemical analysis)

A difference in the two indexes of refraction exhibited by most crystalline solids

Refracts light into two different components (calcite), helps characterize some matter

Separation of light into its components wavelengths (prism)

Describes behavior of a substance when it reacts with another substance

Density and refractive index
Glass: hard, brittle, amorphous, composed of silicon oxides and various metal oxides
Soda (sodium carbonate: Na2CO3), lime (calcium oxide: CaO)

Flat glass used in windows

Boron added, creates heat resistant glass
Pyrex, automobile headlights

Strengthened through rapid heating and cooling as it is made
Instead of shattering, it dices into small squares

2 sheets of glass tempered, bonded with plastic film
Used for windshields in automobiles

Pieces fit together like puzzle (unlikely)
Density and refractive index most widely used
Chemical composition sometime used

Flotation-glass is immersed in bromoform, bromobenzene and mixed in ratio
When glass is suspended, densities are equal

Glass is immersed in liquid medium whose refractive index is changed (temperature) until it equals that of the glass

Bright halo on border of glass, disappears in immersion method when refractive index matches (oil at temperature and glass)

Force>elasticity
Fractured glass reveals informations related to force and direction of impact, useful for reconstruction of events at crime scene
Difficult to determine type of projectile (bullets are exception)

Produce a round, crater shaped hole surrounded by nearly symmetrical pattern of radial and concentric cracks
Hole is wider on exit side of glass

Cracks that extend outward like spokes on a wheel
First cracks to form, form at right angles to impact hole, fracture always terminates at existing line of fracture
Opposite side of impact

Form rough circles around the point of impact
Side of impact

Stress markings on edge of impact hole

Particles of soil sink to the portion of the tube that has a density of equal value and remain suspended, low density is at the top,
Probability is < 1 in 50 of finding 2 soils that are indistinguishable in color, density, and mineral content than originates in 2 locations > 1000 ft

Standard reference collected at various intervals within 100 yards of crime scene, should be collected at alibi location

Any disintegrated surface material (natural or artificial) that lies near the Earth's surface

Topsoil: Mineral horizon, forms at surface, rich organic material, dark in color, generally more course

Subsoil: mineral substance, zone of accululation, lots of clay

Parent material: bedrock, always on bottom (glacial till, lake sediments, basalt)

20% organic material by mass, formed in wetlands (anaerobic conditions) or leaf litter in forested areas

Lighter in color (less clay) than A or B, most common in forested area with lots of rain

Fast moving water, deposits large particles

Water starts to slow, deposits medium sized particles

More fine particles

Most can be differentiated by appearance (color, texture)
Wet soil is darker, must dry first to compare color
Low powered microscopes reveal plant, animal, artificial debris
High powered microscopes reveal mineral content (strongest evidence)