Quick Guide to Units and Symbols

Length (l)

m = meter(s)

cm = centimeter(s) (1 cm = 10^-2 m)

mm = millmeter(s) (1 mm = 10^-3 m)

μm = micrometer(s) (1 μm =10^-6 m) NOT micron or μ

nm = nanometer(s) (1 nm = 10^-9 m)

Å = angstrom(s) (1 Å = 10^-10 m)

pm = picometer(s) (1 pm = 10^-12 m)

Volume (V)

L = liter(s); mL = milliliter(s)

cm³ = cubic centimeter(s)

ų = cubic angstrom(s)

Mass (m)

g = gram(s)

kg = kilogram(s)

mg = milligram(s)

μg = microgram(s)

Density (D or ρ)

g/cm³ = gram(s) per cubic centimeter (please do not use Mg/m³)

Concentration (indicate with square brackets [ ] around chemical symbol, e.g., [Cl^1-])

% = percent; ‰ = per mill

wt% = weight percent; mol% = mole percent; vol% = volume percent

M = molar concentration (1 M = 1 mol/L)

m = molal concentration (1 m = 1 mol/kg)

ppm = parts per million; ppb = parts per billion

Time (t)

s = second(s); min = minute(s); h = hour(s)

Note: day(s), week(s), year(s) spelled out

Ma = million years; Ga = billion years (ago or date)

m.y. = million years; b.y. = billion years (duration)

Pressure (P)

Pa = pascal(s)

kPa = kilopascal(s); MPa = megapascal(s)

GPa = gigapascal(s)

bar or bars (no abbreviation)

kbar = kilobar(s)

atm = atmosphere(s) (not recommended)

Temperature (T)

K = Kelvin(s); °C = degrees Celsius

Frequency (f or η)

Hz = hertz; kHz = kilohertz; MHz = megahertz

Energy

J = joule(s); kJ = kilojoule(s) (preferred)

cal = calorie(s); kcal = kilocalorie(s)

Miller indices-- note that letter symbols are italicized but numberic values are not, e.g., [hkl] but [100]

hkl = diffraction symbol

(hkl) = face symbol

{hkl} = form symbol

[hkl] = edge or zone symbol

Unit-cell measurements

a, b, c = edge lengths; α, β, γ = angles

a, b, c = vectors-- note boldface

Optical measurements:

• dispersion (r, v),
• optic axial angle (2V, 2V_x, 2V_z);
• principal vibration directions (E, O; X, Y, Z);
• refractive indices (n; nε, nω, nα, nβ, nγ where the n's are italic and the Greek characters are subscripts)