Black olives are those types of olive which are picked whilst they are ripe when they turned from their green color.

So can guinea pigs eat black olives at all?

Let’s take a look at their nutritional data and find out more.

In particular, their acidic, water, sugar, fat, salt, calcium, and phosphorus content is of particular interest as far as guinea pigs are concerned.

Nutritional value per 100 g (3.5 oz)
Energy 609 kJ (146 kcal)
Carbohydrates
3.84 g
Sugars 0.54 g
Dietary fiber 3.3 g
Fat
15.32 g
Saturated 2.029 g
Monounsaturated 11.314 g
Polyunsaturated 1.307 g
Protein
1.03 g
Vitamins
Vitamin A equiv.
beta-carotene
lutein zeaxanthin
(3%) 20 μg
(2%) 231 μg
510 μg
Thiamine (B1) (2%) 0.021 mg
Riboflavin (B2) (1%) 0.007 mg
Niacin (B3) (2%) 0.237 mg
Vitamin B6 (2%) 0.031 mg
Folate (B9) (1%) 3 μg
Choline (3%) 14.2 mg
Vitamin E (25%) 3.81 mg
Vitamin K (1%) 1.4 μg
Minerals
Calcium (5%) 52 mg
Iron (4%) 0.49 mg
Magnesium (3%) 11 mg
Phosphorus (1%) 4 mg
Potassium (1%) 42 mg
Sodium (104%) 1556 mg
Other constituents
Water 75.3 g

source wikipedia

As you can see, black olives contain a huge amount of water and fat, a hint of phosphorus and sugar, and a little acidic content and and calcium.

This means that they are not a good food for guinea pigs to eat because of its water and fat content. They may make them sick if they eat them so are a food to avoid feeding them.